feat(accounting): tax window shows all costs (incoming invoices + expenses) alongside revenue

Einnahmen-Ausgaben view for the Milchbüchlein/simple-accounting case:
- taxReportService.getTaxReport now returns a cost side (loadCosts:
  incoming invoices + internal expenses, company- or event-booked,
  schema-guarded) plus a summary (income / costs / result, VAT payable)
- declined/duplicate costs excluded; re-billed costs kept (matching
  re-bill revenue is counted, so the net is correct)
- CSV + PDF exports gain a Costs section and an income/costs/result
  summary; pdf-i18n keys added for all 6 locales (fr/nl/pt/ru machine —
  flag for native review)
- frontend tax page renders the summary card, a costs table (company
  vs event), and a 'verify with Treuhänder' disclaimer
- tax-report tests cover the cost aggregation + zeroed summary when the
  accounting tables are absent; adminCrmAuth test enables the accounting
  master flag the route now requires

fr/nl/pt/ru strings are machine-generated and need native review.

frontend/src/i18n/locales/de.json

@@ -3769,6 +3769,25 @@
     "grandTotalVat": "Gesamt MwSt.",
     "grandTotalGross": "Gesamt Brutto",
     "cancelledFootnote": "{{count}} stornierte Rechnung(en) — Beträge nicht in den Summen enthalten (für lückenlose Nummernfolge dargestellt).",
+    "skontoTooltip": "Mit Skonto bezahlt",
+    "costsTitle": "Kosten (Eingangsrechnungen + Spesen)",
+    "costsDisclaimer": "Diese Einnahmen-Ausgaben-Übersicht ist eine Orientierungshilfe für Ihre Aufzeichnungen (Milchbüchleinrechnung). Vorsteuerabzug und Ergebnis hängen von der steuerlichen Behandlung jeder Kostenposition ab — vor der Einreichung mit Ihrem Treuhänder / der Steuerverwaltung prüfen.",
+    "summary": {
+      "title": "Einnahmen / Ausgaben",
+      "income": "Einnahmen",
+      "costs": "Ausgaben",
+      "result": "Ergebnis",
+      "vatPayable": "MWST-Zahllast (Umsatz- − Vorsteuer)"
+    },
+    "cost": {
+      "source": "Art",
+      "sourceIncoming": "Eingang",
+      "sourceExpense": "Spese",
+      "supplier": "Lieferant / Beschreibung",
+      "taxTreatment": "Steuerliche Behandlung",
+      "company": "Unternehmen",
+      "total": "Summe Kosten"
+    },
     "col": {
       "date": "Datum",
       "invoice": "Rechnung",
@@ -3777,7 +3796,8 @@
       "vatRate": "MwSt %",
       "net": "Netto",
       "vat": "MwSt.",
-      "total": "Brutto"
+      "total": "Brutto",
+      "skonto": "Skonto"
     }
   },
   "quotes": {

frontend/src/i18n/locales/en.json

@@ -3769,6 +3769,25 @@
     "grandTotalVat": "Total VAT",
     "grandTotalGross": "Total gross",
     "cancelledFootnote": "{{count}} cancelled invoice(s) — amounts excluded from totals (shown for audit-trail continuity).",
+    "skontoTooltip": "Paid with Skonto",
+    "costsTitle": "Costs (incoming invoices + expenses)",
+    "costsDisclaimer": "This income/expense overview is a guideline for your records (Einnahmen-Ausgaben-Rechnung). VAT reclaimability and the result figure depend on each cost’s tax treatment — verify with your Treuhänder / tax authority before filing.",
+    "summary": {
+      "title": "Income / costs",
+      "income": "Income",
+      "costs": "Costs",
+      "result": "Result",
+      "vatPayable": "VAT payable (output − input)"
+    },
+    "cost": {
+      "source": "Type",
+      "sourceIncoming": "Incoming",
+      "sourceExpense": "Expense",
+      "supplier": "Supplier / description",
+      "taxTreatment": "Tax treatment",
+      "company": "Company",
+      "total": "Total costs"
+    },
     "col": {
       "date": "Date",
       "invoice": "Invoice",
@@ -3777,7 +3796,8 @@
       "vatRate": "VAT %",
       "net": "Net",
       "vat": "VAT",
-      "total": "Gross"
+      "total": "Gross",
+      "skonto": "Skonto"
     }
   },
   "quotes": {

frontend/src/pages/admin/clients/TaxReportPage.tsx

@@ -143,7 +143,9 @@ export const TaxReportPage: React.FC = () => {
   // rates in the period. With a single rate the breakdown is just a
   // restatement of the grand totals — pure noise.
   const showPerRateBreakdown = (report?.totalsByVatRate.length || 0) > 1;
-  const exportsDisabled = isLoading || isExporting !== null || !report || report.rows.length === 0;
+  const hasCosts = (report?.costs?.rows.length || 0) > 0;
+  const hasAnyData = !!report && (report.rows.length > 0 || hasCosts);
+  const exportsDisabled = isLoading || isExporting !== null || !hasAnyData;
 
   return (
     <div className="space-y-6">
@@ -260,7 +262,7 @@ export const TaxReportPage: React.FC = () => {
             there are 2+ rates in the period (otherwise it duplicates
             the grand totals). Cancelled footnote at the bottom when
             applicable. */}
-        {report && report.rows.length > 0 && (
+        {hasAnyData && report && (
           <Card padding="md">
             <div className="space-y-1.5 text-sm">
               <div className="flex justify-between gap-3">
@@ -283,6 +285,45 @@ export const TaxReportPage: React.FC = () => {
               </div>
             </div>
 
+            {/* Einnahmen-Ausgaben summary (#4): income vs costs vs
+                result. Only when there is a cost side. The result line
+                is the simplified surplus a Milchbüchlein needs; VAT
+                payable is a guideline (depends on each cost's tax
+                treatment — see disclaimer below the cost table). */}
+            {hasCosts && report.summary && (
+              <div className="mt-4 pt-3 border-t border-neutral-200 dark:border-neutral-700">
+                <h2 className="text-xs font-semibold uppercase tracking-wider text-neutral-500 dark:text-neutral-400 mb-2">
+                  {t('taxReport.summary.title', 'Income / costs')}
+                </h2>
+                <div className="space-y-1.5 text-sm">
+                  <div className="flex justify-between gap-3">
+                    <span className="text-neutral-700 dark:text-neutral-300">{t('taxReport.summary.income', 'Income')}</span>
+                    <span className="tabular-nums text-emerald-700 dark:text-emerald-400">
+                      {formatMinor(report.summary.incomeGrossMinor, report.currency, intlLocale)}
+                    </span>
+                  </div>
+                  <div className="flex justify-between gap-3">
+                    <span className="text-neutral-700 dark:text-neutral-300">{t('taxReport.summary.costs', 'Costs')}</span>
+                    <span className="tabular-nums text-rose-700 dark:text-rose-400">
+                      −{formatMinor(report.summary.costGrossMinor, report.currency, intlLocale)}
+                    </span>
+                  </div>
+                  <div className="flex justify-between gap-3 pt-1.5 border-t border-neutral-200 dark:border-neutral-700">
+                    <span className="font-semibold text-neutral-900 dark:text-neutral-100">{t('taxReport.summary.result', 'Result')}</span>
+                    <span className="tabular-nums font-semibold text-neutral-900 dark:text-neutral-100">
+                      {formatMinor(report.summary.resultGrossMinor, report.currency, intlLocale)}
+                    </span>
+                  </div>
+                  <div className="flex justify-between gap-3 text-xs text-neutral-500 dark:text-neutral-400">
+                    <span>{t('taxReport.summary.vatPayable', 'VAT payable (output − input)')}</span>
+                    <span className="tabular-nums">
+                      {formatMinor(report.summary.vatPayableMinor, report.currency, intlLocale)}
+                    </span>
+                  </div>
+                </div>
+              </div>
+            )}
+
             {showPerRateBreakdown && (
               <div className="mt-4 pt-3 border-t border-neutral-200 dark:border-neutral-700">
                 <h2 className="text-xs font-semibold uppercase tracking-wider text-neutral-500 dark:text-neutral-400 mb-2">
@@ -335,7 +376,7 @@ export const TaxReportPage: React.FC = () => {
             </div>
           </div>
         </Card>
-      ) : !report || report.rows.length === 0 ? (
+      ) : !hasAnyData ? (
         <Card padding="lg">
           <p className="text-center text-sm text-neutral-600 dark:text-neutral-400">
             {t('taxReport.empty', 'No invoices in this period.')}
@@ -343,9 +384,10 @@ export const TaxReportPage: React.FC = () => {
         </Card>
       ) : (
         <>
-          {/* Table — full width below the filter + totals row above.
+          {report && report.rows.length > 0 && (
+          /* Table — full width below the filter + totals row above.
               The totals card now lives in the top-right of the page
-              header so this section is purely the invoice list. */}
+              header so this section is purely the invoice list. */
           <Card padding="none">
             {/* Two nested wrappers: the OUTER clips the header row's
                 solid fill so the top corners stay rounded (matches
@@ -436,6 +478,98 @@ export const TaxReportPage: React.FC = () => {
               </div>
             </div>
           </Card>
+          )}
+
+          {/* Cost side (#4) — incoming invoices + expenses, company or
+              event-booked. Shown as its own table beneath the revenue
+              list so the Einnahmen-Ausgaben picture is complete on one
+              page. */}
+          {hasCosts && report && (
+            <Card padding="none">
+              <div className="px-3 pt-3 pb-1">
+                <h2 className="text-sm font-semibold text-neutral-900 dark:text-neutral-100">
+                  {t('taxReport.costsTitle', 'Costs (incoming invoices + expenses)')}
+                </h2>
+              </div>
+              <div className="rounded-xl overflow-hidden">
+                <div className="overflow-x-auto">
+                  <table className="w-full text-sm">
+                    <thead className="bg-neutral-50 dark:bg-neutral-900 text-neutral-700 dark:text-neutral-300">
+                      <tr>
+                        <th className="px-2 py-2 text-right font-medium w-10">#</th>
+                        <th className="px-2 py-2 text-left font-medium whitespace-nowrap">{t('taxReport.col.date', 'Date')}</th>
+                        <th className="px-2 py-2 text-left font-medium whitespace-nowrap">{t('taxReport.cost.source', 'Type')}</th>
+                        <th className="px-2 py-2 text-left font-medium">{t('taxReport.cost.supplier', 'Supplier / description')}</th>
+                        <th className="px-2 py-2 text-left font-medium">{t('taxReport.col.event', 'Event')}</th>
+                        <th className="px-2 py-2 text-left font-medium whitespace-nowrap">{t('taxReport.cost.taxTreatment', 'Tax treatment')}</th>
+                        <th className="px-2 py-2 text-right font-medium whitespace-nowrap">{t('taxReport.col.net', 'Net')}</th>
+                        <th className="px-2 py-2 text-right font-medium whitespace-nowrap">{t('taxReport.col.vat', 'VAT')}</th>
+                        <th className="px-2 py-2 text-right font-medium whitespace-nowrap">{t('taxReport.col.total', 'Gross')}</th>
+                      </tr>
+                    </thead>
+                    <tbody className="divide-y divide-neutral-200 dark:divide-neutral-800 text-neutral-900 dark:text-neutral-100">
+                      {report.costs.rows.map((row, i) => (
+                        <tr key={`${row.source}-${row.id}`}>
+                          <td className="px-2 py-1.5 text-right tabular-nums">{i + 1}</td>
+                          <td className="px-2 py-1.5 whitespace-nowrap tabular-nums">{fmtDate(String(row.date).slice(0, 10))}</td>
+                          <td className="px-2 py-1.5 whitespace-nowrap">
+                            <span className={`inline-block px-1.5 py-0.5 text-[10px] uppercase tracking-wider rounded font-semibold ${
+                              row.source === 'incoming'
+                                ? 'bg-indigo-100 text-indigo-800 dark:bg-indigo-900/40 dark:text-indigo-300'
+                                : 'bg-amber-100 text-amber-800 dark:bg-amber-900/40 dark:text-amber-300'
+                            }`}>
+                              {row.source === 'incoming'
+                                ? t('taxReport.cost.sourceIncoming', 'Incoming')
+                                : t('taxReport.cost.sourceExpense', 'Expense')}
+                            </span>
+                          </td>
+                          <td className="px-2 py-1.5 truncate max-w-[220px]" title={row.supplierLabel || row.description}>
+                            {row.supplierLabel || row.description || '—'}
+                          </td>
+                          <td className="px-2 py-1.5 truncate max-w-[160px]" title={row.eventName}>
+                            {row.eventName || <span className="text-neutral-400 dark:text-neutral-500">{t('taxReport.cost.company', 'Company')}</span>}
+                          </td>
+                          <td className="px-2 py-1.5 whitespace-nowrap text-xs text-neutral-500 dark:text-neutral-400">{row.taxTreatment}</td>
+                          <td className="px-2 py-1.5 text-right tabular-nums whitespace-nowrap">
+                            {formatMinor(row.netMinor, report.currency, intlLocale)}
+                          </td>
+                          <td className="px-2 py-1.5 text-right tabular-nums whitespace-nowrap">
+                            {formatMinor(row.vatMinor, report.currency, intlLocale)}
+                          </td>
+                          <td className="px-2 py-1.5 text-right tabular-nums whitespace-nowrap font-medium">
+                            {formatMinor(row.totalMinor, report.currency, intlLocale)}
+                          </td>
+                        </tr>
+                      ))}
+                    </tbody>
+                    <tfoot className="border-t-2 border-neutral-300 dark:border-neutral-700 font-semibold text-neutral-900 dark:text-neutral-100">
+                      <tr>
+                        <td className="px-2 py-2" colSpan={6}>{t('taxReport.cost.total', 'Total costs')}</td>
+                        <td className="px-2 py-2 text-right tabular-nums whitespace-nowrap">{formatMinor(report.costs.totalNet, report.currency, intlLocale)}</td>
+                        <td className="px-2 py-2 text-right tabular-nums whitespace-nowrap">{formatMinor(report.costs.totalVat, report.currency, intlLocale)}</td>
+                        <td className="px-2 py-2 text-right tabular-nums whitespace-nowrap">{formatMinor(report.costs.totalGross, report.currency, intlLocale)}</td>
+                      </tr>
+                    </tfoot>
+                  </table>
+                </div>
+              </div>
+            </Card>
+          )}
+
+          {/* Legal disclaimer — tax figures are a guideline. Per project
+              rule: any surface touching tax/financial output must point
+              the user at a professional. */}
+          {hasCosts && (
+            <p className="flex items-start gap-2 text-xs text-neutral-500 dark:text-neutral-400">
+              <AlertCircle className="w-4 h-4 flex-shrink-0 mt-0.5" />
+              <span>
+                {t(
+                  'taxReport.costsDisclaimer',
+                  'This income/expense overview is a guideline for your records (Einnahmen-Ausgaben-Rechnung). VAT reclaimability and the result figure depend on each cost’s tax treatment — verify with your Treuhänder / tax authority before filing.',
+                )}
+              </span>
+            </p>
+          )}
         </>
       )}
     </div>

frontend/src/services/taxReport.service.ts

@@ -46,6 +46,47 @@ export interface TaxReportBucket {
   totalMinor: number;
 }
 
+/** A single cost-side line (#4 — Einnahmen-Ausgaben). Either an external
+ *  incoming invoice (`source: 'incoming'`) or an internal expense
+ *  (`source: 'expense'`). Booked to an event (`eventName`) or the
+ *  company (empty `eventName`). */
+export interface TaxReportCostRow {
+  id: number;
+  source: 'incoming' | 'expense';
+  date: string;
+  supplierLabel: string;
+  description: string;
+  eventName: string;
+  disposition: string;
+  taxTreatment: string;
+  status: string;
+  netMinor: number;
+  vatMinor: number;
+  totalMinor: number;
+}
+
+export interface TaxReportCosts {
+  rows: TaxReportCostRow[];
+  totalNet: number;
+  totalVat: number;
+  totalGross: number;
+}
+
+/** Income vs cost vs result summary (minor units). `vatPayableMinor` =
+ *  output VAT − input VAT (a guideline figure; actual MWST filing
+ *  depends on each cost's tax treatment — verify with a Treuhänder). */
+export interface TaxReportSummary {
+  incomeNetMinor: number;
+  incomeVatMinor: number;
+  incomeGrossMinor: number;
+  costNetMinor: number;
+  costVatMinor: number;
+  costGrossMinor: number;
+  resultNetMinor: number;
+  resultGrossMinor: number;
+  vatPayableMinor: number;
+}
+
 export interface TaxReport {
   rows: TaxReportRow[];
   totalsByVatRate: TaxReportBucket[];
@@ -53,6 +94,11 @@ export interface TaxReport {
   grandTotalVat: number;
   grandTotal: number;
   cancelledCount: number;
+  /** Cost side (#4). Present when the accounting tables exist; empty
+   *  otherwise. */
+  costs: TaxReportCosts;
+  /** Income/cost/result summary (#4). */
+  summary: TaxReportSummary;
   currency: string;
   period: { from: string; to: string };
 }