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/styles.scss

@@ -31,6 +31,15 @@ html, body { margin: 0; min-height: 100%; }
 .app-stack > * + * { margin-block-start: var(--rhc-space-max-xl); }
 .app-section { margin-block-start: var(--rhc-space-max-2xl); }
 .app-text-subtle { color: var(--rhc-color-foreground-subtle); }
+/* responsive card grid: cards wrap and stretch, gap from the spacing scale */
+.app-card-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(16rem, 1fr));
+  gap: var(--rhc-space-max-xl);
+  list-style: none;
+  margin: 0;
+  padding: 0;
+}
 
 /* Route transitions (withViewTransitions): cross-fade the routed CONTENT only.
    The chrome gets its own stable view-transition-name so it's lifted out of the