perf: 性能优化与代码质量改进

- 添加4个数据库索引提升查询性能
- 启用ESLint并配置React支持
- 修复ESLint错误（未使用的导入和状态）
- 简化Toast组件UI样式
- 移除重复文件(server.js.backup)
- 清理.gitignore中的.next目录

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

package.json

@@ -15,21 +15,24 @@
     "lint:fix": "eslint server/ frontend/ --fix"
   },
   "dependencies": {
-    "express": "^4.18.2",
-    "better-sqlite3": "^9.2.2",
-    "jsonwebtoken": "^9.0.2",
     "bcryptjs": "^2.4.3",
+    "better-sqlite3": "^9.2.2",
     "cors": "^2.8.5",
-    "dotenv": "^16.3.1"
+    "dotenv": "^16.3.1",
+    "express": "^4.18.2",
+    "jsonwebtoken": "^9.0.2"
   },
   "devDependencies": {
+    "@next/eslint-plugin-next": "^16.2.0",
     "concurrently": "^8.2.2",
     "eslint": "^8.55.0",
+    "eslint-config-prettier": "^9.1.0",
+    "eslint-plugin-node": "^11.1.0",
+    "eslint-plugin-react": "^7.37.5",
+    "eslint-plugin-react-hooks": "^7.0.1",
     "jest": "^29.7.0",
     "nodemon": "^3.0.2",
     "prettier": "^3.1.0",
-    "eslint-config-prettier": "^9.1.0",
-    "eslint-plugin-node": "^11.1.0",
     "supertest": "^6.3.3"
   }
 }