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/herregistratie/ui/herregistratie.page.ts

@@ -0,0 +1,42 @@
+import { Component, computed, inject } from '@angular/core';
+import { PageShellComponent } from '@shared/layout/page-shell/page-shell.component';
+import { AlertComponent } from '@shared/ui/alert/alert.component';
+import { ASYNC } from '@shared/ui/async/async.component';
+import { map } from '@shared/application/remote-data';
+import { BigProfileStore } from '@registratie/application/big-profile.store';
+import { isHerregistratieEligible } from '@registratie/domain/registration.policy';
+import { HerregistratieWizardComponent } from '@herregistratie/ui/herregistratie-wizard/herregistratie-wizard.component';
+
+/** A whole new page built from existing building blocks. Eligibility is a pure
+    domain rule (registration.policy) read from the shared profile state. */
+@Component({
+  selector: 'app-herregistratie-page',
+  imports: [PageShellComponent, AlertComponent, ...ASYNC, HerregistratieWizardComponent],
+  template: `
+    <app-page-shell heading="Herregistratie aanvragen" backLink="/dashboard">
+      <app-async [data]="eligibility()">
+        <ng-template appAsyncLoaded let-eligible>
+          @if (eligible) {
+            <app-alert type="info">
+              Uw huidige registratie verloopt binnenkort. Vraag tijdig herregistratie aan.
+            </app-alert>
+            <div style="margin-top:1.5rem">
+              <app-herregistratie-wizard />
+            </div>
+          } @else {
+            <app-alert type="warning">
+              Voor uw huidige registratiestatus is herregistratie niet mogelijk.
+            </app-alert>
+          }
+        </ng-template>
+      </app-async>
+    </app-page-shell>
+  `,
+})
+export class HerregistratiePage {
+  private store = inject(BigProfileStore);
+  // Derive a boolean RemoteData from the combined profile via map (pure).
+  protected eligibility = computed(() =>
+    map(this.store.profile(), (p) => isHerregistratieEligible(p.registration, new Date())),
+  );
+}