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/ui/spinner/spinner.component.ts

@@ -0,0 +1,28 @@
+import { Component, OnDestroy, OnInit, input, signal } from '@angular/core';
+
+/** Atom: spinner that only appears after `delay` ms — fast responses never
+    flash a spinner, slow ones get feedback. */
+@Component({
+  selector: 'app-spinner',
+  styles: [`
+    :host{display:block}
+    .sp{width:2rem;height:2rem;border-radius:50%;
+        border:3px solid var(--rhc-color-grijs-300,#cad0d6);
+        border-block-start-color:var(--rhc-color-lintblauw-700,#154273);
+        animation:sp 0.8s linear infinite;margin:1.5rem auto}
+    @keyframes sp{to{transform:rotate(360deg)}}
+  `],
+  template: `
+    @if (visible()) {
+      <div class="sp" role="status" aria-label="Bezig met laden"></div>
+    }
+  `,
+})
+export class SpinnerComponent implements OnInit, OnDestroy {
+  delay = input(250);
+  protected visible = signal(false);
+  private timer?: ReturnType<typeof setTimeout>;
+
+  ngOnInit() { this.timer = setTimeout(() => this.visible.set(true), this.delay()); }
+  ngOnDestroy() { clearTimeout(this.timer); }
+}