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/alert/alert.component.ts

@@ -0,0 +1,22 @@
+import { Component, input } from '@angular/core';
+
+type AlertType = 'info' | 'ok' | 'warning' | 'error';
+
+/** Atom: alert/message banner. */
+@Component({
+  selector: 'app-alert',
+  template: `
+    <div
+      class="utrecht-alert rhc-alert"
+      [class.utrecht-alert--info]="type() === 'info'"
+      [class.utrecht-alert--ok]="type() === 'ok'"
+      [class.utrecht-alert--warning]="type() === 'warning'"
+      [class.utrecht-alert--error]="type() === 'error'"
+      role="status">
+      <ng-content />
+    </div>
+  `,
+})
+export class AlertComponent {
+  type = input<AlertType>('info');
+}