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/ui/data-block/data-block.component.ts

@@ -12,7 +12,9 @@ import { HeadingComponent } from '@shared/ui/heading/heading.component';
   selector: 'app-data-block',
   imports: [HeadingComponent],
   template: `
-    @if (heading()) { <app-heading [level]="level()">{{ heading() }}</app-heading> }
+    @if (heading()) {
+      <app-heading [level]="level()">{{ heading() }}</app-heading>
+    }
     <div class="data-block" [class.data-block--stacked]="stacked()">
       <div class="block-wrapper">
         <dl class="mb-0" [attr.aria-label]="ariaLabel() || null">