Restructure into DDD bounded contexts + functional state management

Reorganise from atomic-design-only folders into bounded contexts
(auth / registratie / herregistratie) over a shared kernel, each split into
domain / application / infrastructure / ui layers. Dependencies point inward;
the domain layer is framework-free. Path aliases (@shared/@auth/@registratie/
@herregistratie) make import direction explicit.

State management (Elm-style, native TS, no new deps):
- shared/application/store.ts — createStore(init, update): pure reducer + signal
- shared/application/remote-data.ts — add map/map2/map3/andThen combinators so
  several services fold into one RemoteData; <app-async> gains an [rd] input
- registratie/application/big-profile.store.ts — root singleton combining the
  BIG-register and BRP services via map2 into one state; holds the optimistic
  herregistratie flag shared with the dashboard
- herregistratie: machine gains a WizardMsg union + pure reduce; submit is a
  command that calls infra and dispatches the result, with optimistic update +
  rollback against the shared store
- auth: SessionStore + DigiD adapter + functional route guard; login establishes
  the session, protected routes use canActivate

Rich domain: registration.policy.ts (statusColor/label, herregistratie
eligibility, invariants); BigNummer/Postcode/Uren value objects with smart
constructors. status-badge is now domain-free (colour/label inputs).

Specs for the reducer, RemoteData combinators, and eligibility policy.

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

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

@@ -0,0 +1,29 @@
+import { HttpErrorResponse, HttpInterceptorFn, HttpResponse } from '@angular/common/http';
+import { of, switchMap, throwError, timer } from 'rxjs';
+import { delay } from 'rxjs/operators';
+import { currentScenario } from './scenario';
+
+/**
+ * Demo-only: rewrites the timing/outcome of mock data requests based on
+ * ?scenario= so loading / empty / error states can be shown on demand.
+ * Real requests are untouched.
+ */
+export const scenarioInterceptor: HttpInterceptorFn = (req, next) => {
+  if (!req.url.includes('mock/')) return next(req);
+
+  switch (currentScenario()) {
+    case 'slow':
+      return next(req).pipe(delay(2500));
+    case 'loading':
+      return next(req).pipe(delay(600_000)); // effectively never resolves
+    case 'empty':
+      return of(new HttpResponse({ status: 200, body: [] })).pipe(delay(400));
+    case 'error':
+      return timer(400).pipe(
+        switchMap(() => throwError(() =>
+          new HttpErrorResponse({ status: 500, statusText: 'Demo-fout', url: req.url }))),
+      );
+    default:
+      return next(req);
+  }
+};