chore: update dependencies in package.json and bun.lock, including better-auth to version 1.4.18, and add new packages for improved functionality

Backend/package.json

@@ -20,12 +20,12 @@
     "actions-on-google": "^3.0.0",
     "axios": "^1.13.4",
     "bcrypt": "^6.0.0",
+    "better-auth": "^1.4.18",
     "cors": "^2.8.6",
     "dotenv": "^17.2.4",
     "drizzle-orm": "^0.44.0",
     "express": "^5.2.1",
     "helmet": "^8.1.0",
-    "better-auth": "^1.4.0",
     "minio": "^8.0.6",
     "openai": "^6.18.0",
     "pg": "^8.18.0",