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>

nswag.json

@@ -0,0 +1,29 @@
+{
+  "runtime": "Net80",
+  "documentGenerator": {
+    "fromDocument": {
+      "url": "backend/swagger.json"
+    }
+  },
+  "codeGenerators": {
+    "openApiToTypeScriptClient": {
+      "className": "ApiClient",
+      "moduleName": "",
+      "namespace": "",
+      "template": "Fetch",
+      "promiseType": "Promise",
+      "httpClass": "HttpClient",
+      "useGetBaseUrlMethod": false,
+      "baseUrlTokenName": "API_BASE_URL",
+      "generateClientClasses": true,
+      "generateOptionalParameters": true,
+      "typeScriptVersion": 5.0,
+      "dateTimeType": "String",
+      "nullValue": "Undefined",
+      "generateDtoTypes": true,
+      "typeStyle": "Interface",
+      "markOptionalProperties": true,
+      "output": "src/app/shared/infrastructure/api-client.ts"
+    }
+  }
+}