test(portal-self-service): DigiD-guarded registration submit page (refs #67)

Scaffold libs/ui (NL Design System via Utrecht components) and libs/auth (DigiD OIDC
over angular-auth-oidc-client: mockable AuthService, provider, token interceptor,
authenticated guard). Failing component + axe tests for the RegistrationPage: it must
show the signed-in BSN, submit to the BFF (mocked api-client) and confirm, with no
WCAG 2.1 AA violations. The page is a stub, so the behaviour tests fail; green follows.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/self-service/src/app/registration/registration-page.spec.ts

@@ -0,0 +1,51 @@
+import { signal } from '@angular/core';
+import { fireEvent, render, screen } from '@testing-library/angular';
+import { of } from 'rxjs';
+import { AuthService } from 'auth';
+import { BffApiV1Service } from 'api-client';
+import { axe } from 'vitest-axe';
+import { RegistrationPage } from './registration-page';
+
+class FakeAuth extends AuthService {
+  readonly isAuthenticated = signal(true);
+  readonly bsn = signal<string | undefined>('123456782');
+  login(): void {
+    /* noop */
+  }
+  logout(): void {
+    /* noop */
+  }
+}
+
+function providers(post = vi.fn().mockReturnValue(of({ registrationId: 'reg-9', status: 'Ingediend' }))) {
+  return {
+    post,
+    providers: [
+      { provide: AuthService, useClass: FakeAuth },
+      { provide: BffApiV1Service, useValue: { postSelfServiceRegistrations: post } },
+    ],
+  };
+}
+
+describe('RegistrationPage', () => {
+  it('shows the signed-in BSN', async () => {
+    await render(RegistrationPage, { providers: providers().providers });
+    expect(screen.getByText(/123456782/)).toBeTruthy();
+  });
+
+  it('submits the registration and confirms', async () => {
+    const { post, providers: p } = providers();
+    await render(RegistrationPage, { providers: p });
+
+    fireEvent.click(screen.getByRole('button', { name: /indienen/i }));
+
+    expect(post).toHaveBeenCalledTimes(1);
+    expect(await screen.findByText(/ontvangen/i)).toBeTruthy();
+  });
+
+  it('has no WCAG 2.1 AA violations on the submit page', async () => {
+    const { container } = await render(RegistrationPage, { providers: providers().providers });
+    const results = await axe(container);
+    expect(results.violations).toEqual([]);
+  });
+});