style: format frontend, docs and skills with prettier; add .prettierignore

One-time prettier --write so the new format:check CI gate starts green.
.prettierignore excludes generated (api-client.ts, documentation.json),
vendored (public/cibg-huisstijl), and backend (dotnet format owns it).

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

src/app/shared/infrastructure/api-error.spec.ts

@@ -3,7 +3,9 @@ import { problemDetail, problemFieldErrors } from './api-error';
 
 describe('problemDetail', () => {
   it('extracts the detail from an RFC-7807 ProblemDetails', () => {
-    expect(problemDetail({ detail: 'Afgewezen: 0 uren.', status: 422 }, 'fallback')).toBe('Afgewezen: 0 uren.');
+    expect(problemDetail({ detail: 'Afgewezen: 0 uren.', status: 422 }, 'fallback')).toBe(
+      'Afgewezen: 0 uren.',
+    );
   });
 
   it('falls back when there is no detail', () => {
@@ -15,8 +17,9 @@ describe('problemDetail', () => {
 
 describe('problemFieldErrors (G4 seam)', () => {
   it('maps a ValidationProblemDetails errors dict to first-message-per-field', () => {
-    expect(problemFieldErrors({ errors: { straat: ['Verplicht.'], postcode: ['Ongeldig.', 'x'] } }))
-      .toEqual({ straat: 'Verplicht.', postcode: 'Ongeldig.' });
+    expect(
+      problemFieldErrors({ errors: { straat: ['Verplicht.'], postcode: ['Ongeldig.', 'x'] } }),
+    ).toEqual({ straat: 'Verplicht.', postcode: 'Ongeldig.' });
   });
 
   it('returns {} when there is no errors envelope (the current backend shape)', () => {