Hauptmenue: Gutschriften/Lieferscheine-Gesamtuebersicht (portal-scoped)

Neuer Menuepunkt 'Gutschriften' -> Seite /credit-notes mit Tabelle
aller Belege (Beleg-Nr, Art, Kunde, Vertrag, Betrag, Datum, PDF),
Suche + Pagination.

Neuer Endpoint GET /credit-notes (NICHT staff-only wie die uebrigen
Credit-Note-Endpoints): Staff sieht alle Belege aller Kunden, Portal-
Kunden nur eigene + vertretene (Vollmacht via hasAuthorization).
customerIds kommt aus dem JWT, nicht aus Query/Body -> nicht
manipulierbar. Fuer Portal wird receiptPath aus der Response entfernt
(Belege bleiben staff-only). Route requirePermission contracts:read.

Verifiziert: Staff -> alle Belege; Portal-scoped -> nur eigene, korrekt
zugeordnet.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -14,6 +14,7 @@ import CustomerList from './pages/customers/CustomerList';
 import CustomerDetail from './pages/customers/CustomerDetail';
 import CustomerForm from './pages/customers/CustomerForm';
 import ContractList from './pages/contracts/ContractList';
+import CreditNotesOverview from './pages/CreditNotesOverview';
 import ContractDetail from './pages/contracts/ContractDetail';
 import ContractForm from './pages/contracts/ContractForm';
 import ContractCockpit from './pages/contracts/ContractCockpit';
@@ -200,6 +201,7 @@ function App() {
 
         {/* Contracts */}
         <Route path="contracts" element={<PortalConsentGate><ContractList /></PortalConsentGate>} />
+        <Route path="credit-notes" element={<PortalConsentGate><CreditNotesOverview /></PortalConsentGate>} />
         <Route path="contracts/cockpit" element={<ContractCockpit />} />
         <Route path="contracts/new" element={<ContractForm />} />
         <Route path="contracts/:id" element={<PortalConsentGate><ContractDetail /></PortalConsentGate>} />