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/registratie/infrastructure/duo.adapter.ts

@@ -1,21 +1,21 @@
-import { Injectable } from '@angular/core';
-import { httpResource } from '@angular/common/http';
+import { Injectable, inject, resource } from '@angular/core';
 import { Result, ok, err } from '@shared/kernel/fp';
 import { DuoLookupDto, DuoDiplomaDto, PolicyQuestionDto, ManualDiplomaPolicyDto } from '@registratie/contracts/duo-diplomas.dto';
-
-const EMPTY: DuoLookupDto = { diplomas: [], handmatig: { beroepen: [], policyQuestions: [] } };
+import { ApiClient } from '@shared/infrastructure/api-client';
 
 /**
  * Infrastructure adapter for the DUO diploma lookup, reached only through our own
  * ("BFF-lite") endpoint — the anti-corruption boundary. The response carries the
  * user's diplomas (each with its server-computed beroep + policy questions) and
- * the manual-entry fallback policy. The frontend renders; it does not derive. In
- * this POC the endpoint is a static mock.
+ * the manual-entry fallback policy. The frontend renders; it does not derive.
+ * Data comes from the .NET backend (`GET /api/duo/diplomas`) via the typed client.
  */
 @Injectable({ providedIn: 'root' })
 export class DuoAdapter {
+  private client = inject(ApiClient);
+
   diplomasResource() {
-    return httpResource<DuoLookupDto>(() => 'mock/duo-diplomas.json', { defaultValue: EMPTY });
+    return resource({ loader: () => this.client.diplomas() });
   }
 }