feat(crm): cash-basis revenue + backdatable payment date on mark-paid

Per decision: keep dashboard revenue windows on pure cash basis (recognise
by paid_at for ALL invoices) and give the admin control over paid_at.

- adminDashboard: revert the imported-vs-native split; winSum is paid_at >=
  cutoff for every paid invoice again (clean cash basis).
- BillDetailPage mark-paid dialog: add an optional 'Payment date' field
  (LocalizedDateInput, defaults to today) so a payment can be backdated to
  when it actually arrived. Backend already accepted paidAt end-to-end
  (route validator + markPaid service + payment-log) — only the UI was
  missing. EN/DE 'bills.payment.date' added.

This fixes the collapsed 30=90=365 windows (they were collapsing because
many invoices were marked paid in one session, all stamped 'now').

backend/src/routes/adminDashboard.js

@@ -429,37 +429,25 @@ router.get('/crm-stats', adminAuth, async (req, res) => {
           if (r.status in invoiceCounts) invoiceCounts[r.status] = Number(r.count) || 0;
         }
 
-        // Revenue windows: sum of `paid_amount_minor` for invoices
-        // marked PAID inside the window. Using paid_amount (not total)
-        // so partial payments are tracked accurately. Stornos excluded
-        // — they're never status='paid' in normal flow but the guard
-        // is defensive.
+        // Revenue windows: sum of `paid_amount_minor` for invoices marked
+        // PAID whose payment date (`paid_at`) falls inside the window —
+        // cash-basis recognition (revenue counts when the money arrives).
+        // Using paid_amount (not total) so partial payments are tracked
+        // accurately. Stornos excluded — never status='paid' in normal flow,
+        // the guard is defensive.
         //
-        // Recognition date differs by origin:
-        //   • imported (historical) invoices → recognise on issue_date,
-        //     their true economic date. A year-old imported invoice must
-        //     never land in the rolling "last 30/90 days" window. This is
-        //     robust even for rows imported BEFORE the import route began
-        //     anchoring paid_at to issue_date (commit c6b8cc9) — those
-        //     legacy rows still carry an import-time paid_at, so keying on
-        //     issue_date is what actually fixes them.
-        //   • native invoices → recognise on paid_at (cash-basis).
+        // `paid_at` is admin-controllable, so an old/imported invoice lands
+        // in the right window without any special-casing here: the mark-paid
+        // dialog takes an optional payment date (backdate to when the money
+        // actually arrived) and the historical-import route anchors paid_at
+        // to the invoice's issue_date.
         const winSum = async (cutoff) => {
-          const cutoffDateStr = cutoff.toISOString().slice(0, 10);
           const row = await db('invoices')
             .where('status', 'paid')
+            .where('paid_at', '>=', cutoff)
             .andWhere(function() {
               this.whereNot('kind', 'storno').orWhereNull('kind');
             })
-            .andWhere(function() {
-              this.where(function() {
-                this.whereNotNull('imported_pdf_path')
-                  .andWhere('issue_date', '>=', cutoffDateStr);
-              }).orWhere(function() {
-                this.whereNull('imported_pdf_path')
-                  .andWhere('paid_at', '>=', cutoff);
-              });
-            })
             .sum('paid_amount_minor as total')
             .first();
           return Number(row?.total || 0);

frontend/src/i18n/locales/de.json

@@ -3818,6 +3818,7 @@
     "payment": {
       "paidAt": "Bezahlt am",
       "amount": "Betrag",
+      "date": "Zahlungsdatum",
       "method": "Methode",
       "reference": "Referenz",
       "notes": "Notizen",

frontend/src/i18n/locales/en.json

@@ -3807,6 +3807,7 @@
     "payment": {
       "paidAt": "Date",
       "amount": "Amount",
+      "date": "Payment date",
       "method": "Method",
       "reference": "Reference",
       "notes": "Notes",

frontend/src/pages/admin/bills/BillDetailPage.tsx

@@ -8,7 +8,7 @@ import { useTranslation } from 'react-i18next';
 import { Link, useNavigate, useParams } from 'react-router-dom';
 import { useQuery, useQueryClient } from '@tanstack/react-query';
 import { ArrowLeft, Eye, Send, CheckCircle, BellRing, XCircle, Truck, Edit2, RefreshCw } from 'lucide-react';
-import { Button, Card, Loading, Input } from '../../../components/common';
+import { Button, Card, Loading, Input, LocalizedDateInput } from '../../../components/common';
 import { DocumentLineageCard } from '../../../components/admin/DocumentLineageCard';
 import { billsService } from '../../../services/bills.service';
 import { formatMoney } from '../../../components/admin/LineItemsTable';
@@ -29,6 +29,9 @@ export const BillDetailPage: React.FC = () => {
 
   const [payDialogOpen, setPayDialogOpen] = useState(false);
   const [payAmount, setPayAmount] = useState('');
+  // Optional payment date — defaults to today, backdate it to when the
+  // payment actually arrived. Drives `paid_at` (cash-basis revenue windows).
+  const [payDate, setPayDate] = useState(new Date().toISOString().slice(0, 10));
   const [payMethod, setPayMethod] = useState('');
   const [payReference, setPayReference] = useState('');
   const [payNotes, setPayNotes] = useState('');
@@ -210,6 +213,7 @@ export const BillDetailPage: React.FC = () => {
     try {
       await billsService.markPaid(inv.id, {
         amountMinor: Math.round(Number(payAmount) * 100),
+        paidAt: payDate || undefined,
         paymentMethod: payMethod || undefined,
         reference: payReference || undefined,
         notes: payNotes || undefined,
@@ -218,6 +222,7 @@ export const BillDetailPage: React.FC = () => {
       setPayDialogOpen(false);
       setPayAmount(''); setPayMethod(''); setPayReference(''); setPayNotes('');
       setPayWithSkonto(false);
+      setPayDate(new Date().toISOString().slice(0, 10));
       qc.invalidateQueries({ queryKey: ['invoice', id] });
       toast.success(t('bills.paymentRecordedToast', 'Payment recorded.'));
     } catch (e: any) {
@@ -466,6 +471,14 @@ export const BillDetailPage: React.FC = () => {
             <div className="space-y-3">
               <Input type="number" step="0.01" label={t('bills.payment.amount', 'Amount') as string} value={payAmount}
                 onChange={(e) => setPayAmount(e.target.value)} placeholder={String(outstanding.toFixed(2))} />
+              {/* Optional payment date — drives `paid_at`, which the
+                  dashboard's cash-basis revenue windows key on. Defaults
+                  to today; backdate it to when the payment actually arrived. */}
+              <LocalizedDateInput
+                label={t('bills.payment.date', 'Payment date') as string}
+                value={payDate}
+                onChange={setPayDate}
+              />
               {/* Skonto checkbox (migration 126). Only surfaced when
                   the invoice's payment terms actually offer Skonto —
                   the backend resolves skontoPercent from the snapshot