feat(accounting): unify tax report into one signed, typed, sortable ledger

Replaces the separate revenue + costs tables with a single ledger across the
screen, CSV and PDF. Every row is typed (outgoing invoice / incoming invoice /
expense) and signed — outgoing positive, incoming + expenses negative — so
sorting by value runs income → costs and the column nets toward the Result.

- getTaxReport now returns a `ledger` array (signed, typed, date-sorted);
  legacy rows/costs/summary kept for back-compat.
- Frontend: one sortable table (click Type/Date/Party/Net/VAT/Gross), coloured
  type badges, cancelled rows greyed with lineage badges; Income/Costs/Result
  summary box unchanged.
- CSV + PDF reworked to the same unified, signed layout; PDF totals show
  Income / Costs (negative) / Result.
- i18n: en/de (frontend) + pdf-i18n (en/de real; fr/nl/pt/ru English-fallback,
  flagged for native review).

Build + node --check + JSON parse green.

frontend/src/i18n/locales/de.json

@@ -3966,6 +3966,11 @@
       "company": "Unternehmen",
       "total": "Summe Kosten"
     },
+    "type": {
+      "outgoing": "Ausgangsrechnung",
+      "incoming": "Eingangsrechnung",
+      "expense": "Aufwand"
+    },
     "col": {
       "date": "Datum",
       "invoice": "Rechnung",
@@ -3975,7 +3980,11 @@
       "net": "Netto",
       "vat": "MwSt.",
       "total": "Brutto",
-      "skonto": "Skonto"
+      "skonto": "Skonto",
+      "type": "Typ",
+      "reference": "Referenz",
+      "party": "Kunde / Lieferant",
+      "tax": "Steuer"
     }
   },
   "quotes": {

frontend/src/i18n/locales/en.json

@@ -3966,6 +3966,11 @@
       "company": "Company",
       "total": "Total costs"
     },
+    "type": {
+      "outgoing": "Outgoing invoice",
+      "incoming": "Incoming invoice",
+      "expense": "Expense"
+    },
     "col": {
       "date": "Date",
       "invoice": "Invoice",
@@ -3975,7 +3980,11 @@
       "net": "Net",
       "vat": "VAT",
       "total": "Gross",
-      "skonto": "Skonto"
+      "skonto": "Skonto",
+      "type": "Type",
+      "reference": "Reference",
+      "party": "Customer / supplier",
+      "tax": "Tax"
     }
   },
   "quotes": {