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/auth/application/session.store.ts

@@ -0,0 +1,30 @@
+import { Injectable, computed, inject, signal } from '@angular/core';
+import { Result } from '@shared/kernel/fp';
+import { Session } from '../domain/session';
+import { DigidAdapter } from '../infrastructure/digid.adapter';
+
+/**
+ * Holds the current session for the whole app. Because it is providedIn:'root'
+ * there is exactly one instance — every component that injects it sees the same
+ * session signal, so logging in is instantly visible everywhere (the guard, the
+ * header, etc.). ponytail: in-memory only; a refresh logs you out.
+ */
+@Injectable({ providedIn: 'root' })
+export class SessionStore {
+  private digid = inject(DigidAdapter);
+  private _session = signal<Session | null>(null);
+
+  readonly session = this._session.asReadonly();
+  readonly isAuthenticated = computed(() => this._session() !== null);
+
+  /** Effectful command: authenticate, then store the session on success. */
+  async login(bsn: string): Promise<Result<string, Session>> {
+    const r = await this.digid.authenticate(bsn);
+    if (r.ok) this._session.set(r.value);
+    return r;
+  }
+
+  logout() {
+    this._session.set(null);
+  }
+}