test: 添加完整测试套件（52 个文件，326 个用例）

基于 Vitest 搭建测试基础设施，覆盖后端纯函数、API 路由、
前端 hooks、UI 组件和页面级集成测试。

package.json

@@ -6,7 +6,10 @@
     "dev": "next dev",
     "build": "next build",
     "start": "next start",
-    "lint": "eslint"
+    "lint": "eslint",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "test:coverage": "vitest run --coverage"
   },
   "dependencies": {
     "@prisma/client": "^6.19.2",
@@ -25,14 +28,22 @@
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
+    "@testing-library/user-event": "^14.6.1",
     "@types/bcryptjs": "^2.4.6",
     "@types/canvas-confetti": "^1.9.0",
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
+    "@vitejs/plugin-react": "^5.1.4",
     "eslint": "^9",
     "eslint-config-next": "16.1.6",
+    "jsdom": "^28.1.0",
+    "msw": "^2.12.10",
     "tailwindcss": "^4",
-    "typescript": "^5"
+    "typescript": "^5",
+    "vitest": "^4.0.18",
+    "vitest-mock-extended": "^3.1.0"
   }
 }