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>

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

@@ -0,0 +1,13 @@
+import { Component } from '@angular/core';
+import { RouterModule } from '@angular/router';
+import { NxWelcome } from './nx-welcome';
+
+@Component({
+  imports: [NxWelcome, RouterModule],
+  selector: 'app-root',
+  templateUrl: './app.html',
+  styleUrl: './app.css',
+})
+export class App {
+  protected title = 'self-service';
+}