test(portal-self-service): DigiD-guarded registration submit page (refs #67)

Scaffold libs/ui (NL Design System via Utrecht components) and libs/auth (DigiD OIDC
over angular-auth-oidc-client: mockable AuthService, provider, token interceptor,
authenticated guard). Failing component + axe tests for the RegistrationPage: it must
show the signed-in BSN, submit to the BFF (mocked api-client) and confirm, with no
WCAG 2.1 AA violations. The page is a stub, so the behaviour tests fail; green follows.

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

libs/ui/tsconfig.lib.json

@@ -0,0 +1,26 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "outDir": "../../dist/out-tsc",
+    "declaration": true,
+    "declarationMap": true,
+    "inlineSources": true,
+    "types": []
+  },
+  "include": ["src/**/*.ts"],
+  "exclude": [
+    "src/**/*.spec.ts",
+    "src/**/*.test.ts",
+    "vite.config.ts",
+    "vite.config.mts",
+    "vitest.config.ts",
+    "vitest.config.mts",
+    "src/**/*.test.tsx",
+    "src/**/*.spec.tsx",
+    "src/**/*.test.js",
+    "src/**/*.spec.js",
+    "src/**/*.test.jsx",
+    "src/**/*.spec.jsx",
+    "src/test-setup.ts"
+  ]
+}