Fix MongoDB connection issue in production builds

Prevent database disconnection in dbDisconnect() to avoid "Client must be connected" errors in production. The connection pool handles cleanup automatically.

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

src/utils/db.ts

@@ -29,9 +29,7 @@ export const dbConnect = async () => {
 };
 
 export const dbDisconnect = async () => {
-  if (process.env.NODE_ENV === 'development') return;
-  if (mongoConnection.isConnected === 0) return;
-
-  await mongoose.disconnect();
-  mongoConnection.isConnected = 0;
+  // Don't disconnect in production to avoid "Client must be connected" errors
+  // The connection pool will handle connection cleanup automatically
+  return;
 };