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/button/button.component.ts

@@ -0,0 +1,26 @@
+import { Component, input } from '@angular/core';
+
+type Variant = 'primary' | 'secondary' | 'subtle' | 'danger';
+
+/** Atom: button. Thin wrapper over the Utrecht/RHC button CSS. */
+@Component({
+  selector: 'app-button',
+  template: `
+    <button
+      [type]="type()"
+      [disabled]="disabled()"
+      class="utrecht-button rhc-button"
+      [class.utrecht-button--primary-action]="variant() === 'primary'"
+      [class.utrecht-button--secondary-action]="variant() === 'secondary'"
+      [class.utrecht-button--subtle]="variant() === 'subtle'"
+      [class.utrecht-button--danger]="variant() === 'danger'"
+      [class.utrecht-button--disabled]="disabled()">
+      <ng-content />
+    </button>
+  `,
+})
+export class ButtonComponent {
+  variant = input<Variant>('primary');
+  type = input<'button' | 'submit'>('button');
+  disabled = input(false);
+}

src/app/shared/ui/button/button.stories.ts

@@ -0,0 +1,19 @@
+import type { Meta, StoryObj } from '@storybook/angular';
+import { ButtonComponent } from './button.component';
+
+const meta: Meta<ButtonComponent> = {
+  title: 'Atoms/Button',
+  component: ButtonComponent,
+  render: (args) => ({
+    props: args,
+    template: `<app-button [variant]="variant" [type]="type" [disabled]="disabled">Knop</app-button>`,
+  }),
+};
+export default meta;
+type Story = StoryObj<ButtonComponent>;
+
+export const Primary: Story = { args: { variant: 'primary' } };
+export const Secondary: Story = { args: { variant: 'secondary' } };
+export const Subtle: Story = { args: { variant: 'subtle' } };
+export const Danger: Story = { args: { variant: 'danger' } };
+export const Disabled: Story = { args: { variant: 'primary', disabled: true } };