test: install Vitest and configure frontend test runner

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

neode-ui/package.json

@@ -6,6 +6,8 @@
   "scripts": {
     "start": "./start-dev.sh",
     "stop": "./stop-dev.sh",
+    "test": "vitest run",
+    "test:watch": "vitest",
     "dev": "vite",
     "dev:mock": "concurrently \"node mock-backend.js\" \"VITE_AIUI_URL=http://localhost:5173 vite\" \"cd ../../AIUI && pnpm dev 2>/dev/null || echo '[AIUI] Not found at ../../AIUI — chat will show placeholder'\"",
     "dev:real": "echo 'Start backend: cd ../core && cargo run --release' && vite",
@@ -30,6 +32,9 @@
   },
   "devDependencies": {
     "@types/node": "^24.10.0",
+    "@vue/test-utils": "^2.4.6",
+    "jsdom": "^25.0.1",
+    "vitest": "^3.1.1",
     "@vite-pwa/assets-generator": "^1.0.2",
     "@vitejs/plugin-vue": "^6.0.1",
     "@vue/tsconfig": "^0.8.1",