feat(portal): 'Documenten aanleveren' action on the self-service page (refs #102)

After submitting, the zorgprofessional supplies their documents; the page posts to
the BFF keyed by the reference and confirms ("Uw documenten zijn aangeleverd"), with
a surfaced failure + retry. The registration e2e provides documents before the
behandelaar step, since the process now parks at WachtOpDocumenten first.

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

apps/self-service/src/app/registration/registration-page.html

@@ -11,6 +11,24 @@
         <p utrecht-paragraph role="status">
           Uw registratie is ontvangen. Referentie: {{ reference() }}.
         </p>
+        @if (documentsProvided()) {
+          <p utrecht-paragraph role="status">Uw documenten zijn aangeleverd.</p>
+        } @else {
+          @if (provideDocumentsFailed()) {
+            <p utrecht-paragraph role="alert">
+              Het aanleveren van uw documenten is niet gelukt. Probeer het opnieuw.
+            </p>
+          }
+          <button
+            utrecht-button
+            appearance="primary-action-button"
+            type="button"
+            [disabled]="providingDocuments()"
+            (click)="provideDocuments()"
+          >
+            Documenten aanleveren
+          </button>
+        }
         @if (withdrawFailed()) {
           <p utrecht-paragraph role="alert">
             Het intrekken van uw registratie is niet gelukt. Probeer het opnieuw.

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

@@ -26,6 +26,9 @@ export class RegistrationPage {
   protected readonly withdrawing = signal(false);
   protected readonly withdrawn = signal(false);
   protected readonly withdrawFailed = signal(false);
+  protected readonly providingDocuments = signal(false);
+  protected readonly documentsProvided = signal(false);
+  protected readonly provideDocumentsFailed = signal(false);
 
   submit(): void {
     this.submitting.set(true);
@@ -44,6 +47,26 @@ export class RegistrationPage {
     });
   }
 
+  provideDocuments(): void {
+    const reference = this.reference();
+    if (!reference) {
+      return;
+    }
+    this.providingDocuments.set(true);
+    this.provideDocumentsFailed.set(false);
+    this.bff.postSelfServiceRegistrationsIdDocuments(reference).subscribe({
+      next: () => {
+        this.documentsProvided.set(true);
+        this.providingDocuments.set(false);
+      },
+      // Surface the failure instead of swallowing it: keep the action so the user can retry.
+      error: () => {
+        this.provideDocumentsFailed.set(true);
+        this.providingDocuments.set(false);
+      },
+    });
+  }
+
   withdraw(): void {
     const reference = this.reference();
     if (!reference) {