feat: update dependencies and add dotenv, express-rate-limit, and zod; enhance adminSchemas validation

backend/package.json

@@ -13,9 +13,12 @@
     "bcrypt": "^6.0.0",
     "better-sqlite3": "^11.9.1",
     "cors": "^2.8.5",
+    "dotenv": "^16.4.7",
     "express": "^5.1.0",
+    "express-rate-limit": "^7.5.0",
     "jsonwebtoken": "^9.0.2",
-    "nodemailer": "^7.0.3"
+    "nodemailer": "^7.0.3",
+    "zod": "^3.24.2"
   },
   "devDependencies": {
     "@types/bcrypt": "^5.0.2",