refactor: rename Application → Aanvraag across the wire (Step 1/8)

The wire said Application, the domain said Aanvraag — one aggregate with
two names at every hop. Rename the backend DTOs and the /applications
route to /aanvragen, regenerate the typed client, and rename the frontend
adapter/store to match.

Renamed: ApplicationSummaryDto/DetailDto, CreateApplicationRequest,
SubmitApplicationRequest/Response → Aanvraag* equivalents;
ApplicationsAdapter/Store → AanvragenAdapter/Store;
applications.adapter.ts/applications.store.ts → aanvragen.*.

Left untouched: the admin Case/Zaak vocabulary (/admin/cases,
AdminCasesStore) — a separate read model, not part of this rename; the
internal BigRegister.Domain.Applications namespace and the Applications
EF table (renaming those needs a new EF migration, out of scope here).

Part of the dashboard-readability refactor (see the approved plan).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/src/BigRegister.Api/Data/DocumentStore.cs

@@ -43,7 +43,7 @@ public static class DocumentStore
   /// SeedData.Registration.BigNummer ("19012345601", 11 digits — the seeded doctor's BIG-nummer,
   /// a different Dutch identifier scheme). Previously this constant reused that BigNummer value
   /// as a stand-in BSN, which is invalid Dutch-BSN shape: harmless against the local store, but
-  /// a real OpenZaak instance rejects it outright — GET /api/v1/applications 500s (`inpBsn` query
+  /// a real OpenZaak instance rejects it outright — GET /api/v1/aanvragen 500s (`inpBsn` query
   /// filter validation) and every submit's rol-creation POST fails (`inpBsn` max_length) once
   /// Zgw:Enabled=true. Not "111222333" or "999888777" — both already mean a different fixture
   /// identity (the OpenZaak-harness/unit-test caller, and ApplicationTests' "other citizen").