feat(api-client): expose the generated BFF client + repeatable generate target (refs #66)

The lib barrel exports the generated BffApiV1Service + models (SubmitAccepted,
OpenbaarEntry), so the app can inject a typed client for the BFF. Add an
'api-client:generate' target (orval) to regenerate from services/bff/openapi.json;
generation is idempotent. Tests (HttpClientTesting) now pass: POST /self-service/
registrations and GET /openbaar/register with the query, mapping typed responses.

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

libs/api-client/src/lib/bff-api.spec.ts

@@ -8,7 +8,7 @@ import {
   BffApiV1Service,
   type OpenbaarEntry,
   type SubmitAccepted,
-} from 'api-client';
+} from '../index';
 
 describe('BffApiV1Service (generated from services/bff/openapi.json)', () => {
   let service: BffApiV1Service;