feat(T02): vehicle management + mobile.de push + vehicle UI

- Vehicle model: 25+ fields, 5 vehicle types, soft-delete
- Vehicle CRUD: 7 API endpoints with JWT auth, filter/sort/paginate
- mobile.de: push/update/delete listings, field mapping, retry logic
- MobileDeListing model for sync status tracking
- Frontend: VehicleList, VehicleForm, VehicleDetail, MobileDeStatus
- 73 backend tests (82% coverage), 16 frontend tests

frontend/app/[locale]/fahrzeuge/neu/page.tsx

@@ -0,0 +1,10 @@
+import { VehicleForm } from '@/components/vehicles/VehicleForm';
+
+export default function NeuesFahrzeugPage() {
+  return (
+    <div className="max-w-2xl mx-auto p-6">
+      <h1 className="text-2xl font-bold text-text mb-6">Neues Fahrzeug</h1>
+      <VehicleForm mode="create" />
+    </div>
+  );
+}