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/infrastructure/digid.adapter.ts

@@ -0,0 +1,15 @@
+import { Injectable } from '@angular/core';
+import { Result, ok, err } from '@shared/kernel/fp';
+import { Session } from '../domain/session';
+
+/** Infrastructure: talks to the (mock) DigiD identity provider. */
+@Injectable({ providedIn: 'root' })
+export class DigidAdapter {
+  // ponytail: fake DigiD — any 9-digit BSN authenticates to a fixed identity.
+  // Swap for a real OIDC redirect flow when there's a backend.
+  async authenticate(bsn: string): Promise<Result<string, Session>> {
+    const t = bsn.trim();
+    if (!/^\d{9}$/.test(t)) return err('Voer een geldig BSN van 9 cijfers in.');
+    return ok({ bsn: t, naam: 'Dr. A. (Anna) de Vries' });
+  }
+}