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/app.routes.ts

@@ -1,3 +1,7 @@
 import { Route } from '@angular/router';
+import { authenticatedGuard } from 'auth';
+import { RegistrationPage } from './registration/registration-page';
 
-export const appRoutes: Route[] = [];
+export const appRoutes: Route[] = [
+  { path: '', component: RegistrationPage, canActivate: [authenticatedGuard] },
+];