Add ASP.NET Core backend hosting business rules; FE consumes via typed client

Move the authoritative business rules off the frontend into a real backend,
realising the BFF-lite + decision-DTO design (ADR-0001) that until now lived
only in static mock JSON.

Backend (backend/):
- ASP.NET Core (.NET 10) minimal API, contract-first, Swagger UI at /swagger.
- DDD Domain/ rules layer: profession derivation + applicable policy questions
  (DiplomaRules), herregistratie eligibility + reason (HerregistratieRule),
  scholing threshold (IntakePolicy), submit rejections + reference generation
  (SubmissionRules). In-memory seeded data, ProblemDetails (RFC 7807) errors.
- 27 xUnit tests: rule units + endpoint integration incl. BRP no-address and
  DUO not-found fallbacks and 422 submit paths.

Frontend (only infrastructure/ + contracts/ change, as the architecture promised):
- NSwag-generated typed client (api-client.ts), routed through Angular HttpClient
  via a small fetch adapter so the ?scenario= interceptor still applies.
- GET adapters use resource({ loader: client.x }); submit commands call the client
  and map ProblemDetails -> err. The hardcoded uren==0 / manual-diploma rules are
  deleted (now server-side). Domain, stores, UI and format validators unchanged.
- Deleted the now-dead public/mock/*.json.

Tooling/docs:
- npm start proxies /api -> backend; npm run gen:api regenerates the client;
  docker compose up runs both (bind mounts use :z for SELinux/Fedora).
- backend/README.md walkthrough: adding a policy question is a one-file backend
  change, no FE change, no client regen. Updated CLAUDE.md + ARCHITECTURE.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/shared/infrastructure/scenario.interceptor.ts

@@ -4,12 +4,12 @@ import { delay } from 'rxjs/operators';
 import { currentScenario } from './scenario';
 
 /**
- * Demo-only: rewrites the timing/outcome of mock data requests based on
+ * Demo-only: rewrites the timing/outcome of API data requests based on
  * ?scenario= so loading / empty / error states can be shown on demand.
- * Real requests are untouched.
+ * Non-API requests are untouched.
  */
 export const scenarioInterceptor: HttpInterceptorFn = (req, next) => {
-  if (!req.url.includes('mock/')) return next(req);
+  if (!req.url.includes('/api/')) return next(req);
 
   switch (currentScenario()) {
     case 'slow':
@@ -17,7 +17,8 @@ export const scenarioInterceptor: HttpInterceptorFn = (req, next) => {
     case 'loading':
       return next(req).pipe(delay(600_000)); // effectively never resolves
     case 'empty':
-      return of(new HttpResponse({ status: 200, body: [] })).pipe(delay(400));
+      // '[]' so the typed client parses it to an empty array (notes → Empty state).
+      return of(new HttpResponse({ status: 200, body: '[]' })).pipe(delay(400));
     case 'error':
       return timer(400).pipe(
         switchMap(() => throwError(() =>