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>

nx.json

@@ -0,0 +1,120 @@
+{
+  "$schema": "./node_modules/nx/schemas/nx-schema.json",
+  "namedInputs": {
+    "default": [
+      "{projectRoot}/**/*",
+      "sharedGlobals"
+    ],
+    "production": [
+      "default",
+      "!{projectRoot}/.eslintrc.json",
+      "!{projectRoot}/eslint.config.mjs",
+      "!{projectRoot}/**/?(*.)+(spec|test).[jt]s?(x)?(.snap)",
+      "!{projectRoot}/tsconfig.spec.json",
+      "!{projectRoot}/src/test-setup.[jt]s",
+      "!{projectRoot}/jest.config.[jt]s",
+      "!{projectRoot}/test-setup.[jt]s"
+    ],
+    "sharedGlobals": []
+  },
+  "targetDefaults": {
+    "@angular/build:application": {
+      "cache": true,
+      "dependsOn": [
+        "^build"
+      ],
+      "inputs": [
+        "production",
+        "^production"
+      ]
+    },
+    "@nx/eslint:lint": {
+      "cache": true,
+      "inputs": [
+        "default",
+        "^default",
+        "{workspaceRoot}/.eslintrc.json",
+        "{workspaceRoot}/.eslintignore",
+        "{workspaceRoot}/eslint.config.mjs",
+        "{workspaceRoot}/tools/eslint-rules/**/*"
+      ]
+    },
+    "@nx/esbuild:esbuild": {
+      "cache": true,
+      "dependsOn": [
+        "^build"
+      ],
+      "inputs": [
+        "production",
+        "^production"
+      ]
+    },
+    "@nx/js:tsc": {
+      "cache": true,
+      "dependsOn": [
+        "^build"
+      ],
+      "inputs": [
+        "production",
+        "^production"
+      ]
+    },
+    "@nx/vitest:test": {
+      "cache": true,
+      "inputs": [
+        "default",
+        "^production"
+      ]
+    },
+    "@angular/build:unit-test": {
+      "cache": true,
+      "inputs": [
+        "default",
+        "^production"
+      ]
+    }
+  },
+  "plugins": [
+    {
+      "plugin": "@nx/eslint/plugin",
+      "options": {
+        "targetName": "lint"
+      }
+    },
+    {
+      "plugin": "@nx/vite/plugin",
+      "options": {
+        "buildTargetName": "build",
+        "serveTargetName": "serve",
+        "devTargetName": "dev",
+        "previewTargetName": "preview",
+        "serveStaticTargetName": "serve-static",
+        "typecheckTargetName": "typecheck",
+        "buildDepsTargetName": "build-deps",
+        "watchDepsTargetName": "watch-deps"
+      }
+    },
+    {
+      "plugin": "@nx/vitest",
+      "options": {
+        "testTargetName": "vite:test"
+      }
+    }
+  ],
+  "generators": {
+    "@nx/angular:application": {
+      "e2eTestRunner": "playwright",
+      "linter": "eslint",
+      "style": "css",
+      "unitTestRunner": "vitest-analog"
+    },
+    "@nx/angular:library": {
+      "linter": "eslint",
+      "unitTestRunner": "vitest-analog"
+    },
+    "@nx/angular:component": {
+      "style": "css"
+    }
+  },
+  "analytics": false
+}