feat(portal-self-service): implement the DigiD registration submit page (refs #67)

RegistrationPage shows the signed-in BSN and submits to the BFF via the generated
api-client, confirming with the returned reference; built from NL Design System
(Utrecht) components. Wire the guarded route + app providers (DigiD OIDC + token
interceptor + HttpClient), the NL DS theme, and lang=nl. Component tests
(Testing Library) + axe (WCAG 2.1 AA) pass; a guard test covers libs/auth. Replace
the demo eslint depConstraints (scope:shop/shared) with a permissive default.

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

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

@@ -44,8 +44,15 @@ describe('RegistrationPage', () => {
   });
 
   it('has no WCAG 2.1 AA violations on the submit page', async () => {
+    // The portal is Dutch; the real index.html sets lang. Set it here so the document-level
+    // html-has-lang rule reflects the app, not the bare jsdom document.
+    document.documentElement.lang = 'nl';
     const { container } = await render(RegistrationPage, { providers: providers().providers });
-    const results = await axe(container);
+
+    const results = await axe(container, {
+      runOnly: { type: 'tag', values: ['wcag2a', 'wcag2aa', 'wcag21a', 'wcag21aa'] },
+    });
+
     expect(results.violations).toEqual([]);
   });
 });