🔒 Firestore permission denied — fix your rules:

1. Open Firebase Console → your project
2. Firestore Database → Rules tab
3. Replace the rules with the snippet below and click Publish

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /rooms/{roomId} {
      allow read, write: if true;
    }
    match /rooms/{roomId}/messages/{messageId} {
      allow read, write: if true;
    }
    match /profiles/{userId} {
      allow read, write: if request.auth != null
                         && request.auth.uid == userId;
    }
  }
}