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.ts

@@ -1,9 +1,33 @@
-import { Component } from '@angular/core';
+import { Component, inject, signal } from '@angular/core';
+import { BffApiV1Service, type SubmitAccepted } from 'api-client';
+import { AuthService } from 'auth';
+import { UtrechtComponentsModule } from 'ui';
 
-// STUB (red): no bsn, no submit — the component/axe tests fail until the green commit.
+/**
+ * The self-service submit page: a signed-in zorgprofessional confirms and submits their BIG
+ * registration. The bsn comes from the DigiD token (not a form field), so this is a confirm-and-
+ * submit flow that posts to the BFF and shows the returned reference (ADR-0010; S-08c).
+ */
 @Component({
   selector: 'app-registration-page',
-  imports: [],
-  template: '',
+  imports: [UtrechtComponentsModule],
+  templateUrl: './registration-page.html',
 })
-export class RegistrationPage {}
+export class RegistrationPage {
+  private readonly auth = inject(AuthService);
+  private readonly bff = inject(BffApiV1Service);
+
+  protected readonly bsn = this.auth.bsn;
+  protected readonly submitting = signal(false);
+  protected readonly reference = signal<string | undefined>(undefined);
+  protected readonly submitted = signal(false);
+
+  submit(): void {
+    this.submitting.set(true);
+    this.bff.postSelfServiceRegistrations().subscribe((accepted: SubmitAccepted) => {
+      this.reference.set(accepted.registrationId);
+      this.submitted.set(true);
+      this.submitting.set(false);
+    });
+  }
+}