test(web): 添加 vitest 单元测试基础设施和初始测试用例

- 安装 vitest + @testing-library/react + @testing-library/jest-dom + jsdom
- 创建 vitest.config.ts (jsdom 环境, 全局 API, e2e 目录排除)
- 创建 test/setup.ts (@testing-library/jest-dom 匹配器)
- 添加 29 个测试用例: health 常量 (14), useThemeMode hook (2), StatusTag 组件 (13)

apps/web/package.json

@@ -8,6 +8,7 @@
     "build": "tsc -b && vite build",
     "lint": "eslint .",
     "preview": "vite preview",
+    "test": "vitest",
     "test:e2e": "playwright test",
     "test:e2e:ui": "playwright test --ui"
   },
@@ -29,6 +30,8 @@
     "@eslint/js": "^9.39.4",
     "@playwright/test": "^1.52.0",
     "@tailwindcss/vite": "^4.2.2",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
     "@types/node": "^24.12.2",
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
@@ -37,9 +40,11 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.5.2",
     "globals": "^17.4.0",
+    "jsdom": "^29.0.2",
     "tailwindcss": "^4.2.2",
     "typescript": "~6.0.2",
     "typescript-eslint": "^8.58.0",
-    "vite": "^8.0.4"
+    "vite": "^8.0.4",
+    "vitest": "^4.1.5"
   }
 }