feat: add Zod input validation

Author: Shreyanshi210205

backend/package-lock.json

@@ -20,13 +20,16 @@
     "express": "^5.1.0",
     "jsonwebtoken": "^9.0.2",
     "mongodb": "^6.20.0",
-    "mongoose": "^8.19.2"
+    "mongoose": "^8.19.2",
+    "socket.io": "^4.8.1",
+    "zod": "^4.1.12"
   },
   "devDependencies": {
     "@types/bcryptjs": "^2.4.6",
     "@types/express": "^5.0.3",
     "@types/jsonwebtoken": "^9.0.10",
     "@types/node": "^24.9.1",
+    "@types/socket.io": "^3.0.1",
     "nodemon": "^3.1.10",
     "ts-node": "^10.9.2",
     "ts-node-dev": "^2.0.0",