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>

backend/src/BigRegister.Api/Data/SeedData.cs

@@ -0,0 +1,42 @@
+using BigRegister.Domain.Diplomas;
+using BigRegister.Domain.People;
+using BigRegister.Domain.Registrations;
+
+namespace BigRegister.Api.Data;
+
+/// <summary>
+/// In-memory seeded synthetic data — no DB, no real BRP/DUO. Stands in for the
+/// upstream systems so the API behaves like production for a demo.
+/// </summary>
+public static class SeedData
+{
+    public static readonly Registration Registration = new(
+        BigNummer: "19012345601",
+        Naam: "Dr. A. (Anna) de Vries",
+        Beroep: "Arts",
+        Registratiedatum: new DateOnly(2012, 9, 1),
+        Geboortedatum: new DateOnly(1985, 3, 14),
+        Status: new RegistrationStatus(StatusTag.Geregistreerd, HerregistratieDatum: new DateOnly(2027, 3, 1)));
+
+    public static readonly Person Person = new(
+        Naam: "Dr. A. (Anna) de Vries",
+        Geboortedatum: new DateOnly(1985, 3, 14),
+        Adres: new Adres("Lange Voorhout 9", "2514 EA", "Den Haag"));
+
+    /// <summary>The address BRP returns for the seeded citizen.</summary>
+    public static readonly Adres BrpAddress = Person.Adres;
+
+    public static readonly IReadOnlyList<Diploma> Diplomas = new[]
+    {
+        new Diploma("d1", "Geneeskunde", "Universiteit Leiden", 2011, "geneeskunde", Engelstalig: false),
+        new Diploma("d2", "Medicine (MBChB)", "University of Edinburgh", 2013, "geneeskunde", Engelstalig: true),
+        new Diploma("d3", "HBO-Verpleegkunde", "Hogeschool Utrecht", 2016, "verpleegkunde", Engelstalig: false),
+    };
+
+    public static readonly IReadOnlyList<(string Type, string Omschrijving, string Datum)> Notes = new[]
+    {
+        ("Specialisme", "Huisartsgeneeskunde", "2016-04-12"),
+        ("Aantekening", "Erkend opleider huisartsgeneeskunde", "2019-01-08"),
+        ("Specialisme", "Spoedeisende hulp (kaderopleiding)", "2021-06-30"),
+    };
+}