test(portal-self-service): self-service portal placeholder renders (refs #65)

Bootstrap the Nx (pnpm) workspace at the repo root with the self-service Angular
app (standalone + signals, Vitest via @angular/build, ESLint) — the frontend
foundation. Nx is scoped to apps/+libs/ only; the .NET services stay on
dotnet/Makefile (no @nx/docker inference). A failing test asserts the app renders
a 'Zelfservice' heading; it still shows the generated Nx welcome page, so it fails.
Green commit implements the placeholder.

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

.gitignore

@@ -35,3 +35,18 @@ site/
 # OS
 .DS_Store
 Thumbs.db
+
+# ── Frontend (Nx / Angular / pnpm) ──
+node_modules/
+dist/
+tmp/
+out-tsc/
+/coverage
+.angular/
+.nx/cache
+.nx/workspace-data
+.nx/self-healing
+.nx/migrate-runs
+.nx/polygraph
+vite.config.*.timestamp*
+vitest.config.*.timestamp*