feat(sprint8): Phase 2 — Treasury frontend + PDF receipts

Backend:
- ReceiptPdfService: Generates Quittung PDF per payment (OpenPDF, A4)
- FinancialReportService: Annual financial report PDF (Jahresabschluss)
- FinanceController: Added receipt download, annual report, CSV export endpoints
- Portal receipt download with member ownership verification

Frontend:
- src/services/finance.ts: Complete React Query service (types, hooks, mutations)
- /finance: Dashboard with KPI cards, recent transactions, outstanding members
- /finance/payments: Payment list with filtering, void, receipt download
- /finance/kassenbuch: Kassenbuch ledger with date range, CSV export
- /finance/fee-schedules: Fee schedule CRUD with interval management
- /finance/reports: Annual report PDF download
- /portal/finance: Member self-service balance + payment history + receipts

Navigation & i18n:
- Added Finanzen (Wallet icon) to admin sidebar
- Portal finance page for member payments
- Comprehensive de.json + en.json finance keys (~100 translations)

cannamanage-frontend/src/data/navigations.ts

@@ -39,6 +39,11 @@ export const navigationsData: NavigationType[] = [
         href: "/info-board",
         iconName: "Megaphone",
       },
+      {
+        title: "Finanzen",
+        href: "/finance",
+        iconName: "Wallet",
+      },
       {
         title: "Kalender",
         href: "/calendar",