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>

.prettierignore

@@ -0,0 +1,18 @@
+# Build output & caches
+dist/
+storybook-static/
+coverage/
+.angular/
+
+# Lockfile
+package-lock.json
+
+# Generated — owned by their generators, not prettier
+documentation.json
+src/app/shared/infrastructure/api-client.ts
+
+# Vendored design system (CIBG Huisstijl)
+public/cibg-huisstijl/
+
+# Backend is formatted by `dotnet format`, not prettier
+backend/