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/application/store.ts

@@ -0,0 +1,29 @@
+import { Signal, signal } from '@angular/core';
+
+/**
+ * A tiny "Elm-style" store. The whole idea: all state lives in ONE value
+ * (the Model). The only way to change it is to send a message (Msg) to a PURE
+ * function `update(model, msg)` that returns the next Model. Nothing else
+ * mutates state, so to understand the app you only read the update function.
+ *
+ * Side effects (HTTP, timers) do NOT go in `update` — that stays pure and easy
+ * to test. Instead, effectful "command" functions call the network and then
+ * `dispatch` a message describing what happened (e.g. Loaded / Failed).
+ */
+export interface Store<Model, Msg> {
+  /** The current state, as a read-only Angular signal. */
+  readonly model: Signal<Model>;
+  /** Send a message; the model becomes update(model, msg). */
+  dispatch(msg: Msg): void;
+}
+
+export function createStore<Model, Msg>(
+  init: Model,
+  update: (model: Model, msg: Msg) => Model,
+): Store<Model, Msg> {
+  const model = signal(init);
+  return {
+    model: model.asReadonly(),
+    dispatch: (msg) => model.set(update(model(), msg)),
+  };
+}