refactor: modularize backend security and observability

backend/package.json

@@ -4,7 +4,7 @@
   "description": "玩玩云 - 云存储管理平台后端服务",
   "main": "server.js",
   "engines": {
-    "node": ">=20 <25"
+    "node": ">=20.19 <25"
   },
   "scripts": {
     "start": "node server.js",
@@ -33,11 +33,14 @@
     "cors": "^2.8.5",
     "dotenv": "^16.3.1",
     "express": "^4.18.2",
+    "express-async-errors": "3.1.1",
+    "express-rate-limit": "8.6.1",
     "express-validator": "^7.3.0",
     "jsonwebtoken": "^9.0.2",
     "lodash": "^4.17.23",
     "multer": "^2.2.0",
     "nodemailer": "^9.0.3",
+    "pino": "10.3.1",
     "svg-captcha": "^1.4.0"
   }
 }