fix: resolve Dart analysis errors and format code

- Fixed unused field warning in phone_input_screen.dart
- Resolved undefined getter 'isoCode' by removing unused code
- Fixed undefined class 'User' error by adding proper Firebase import in user_model.dart
- Ran dart format to ensure consistent code style across all files
- All analyzer issues are now resolved

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/app.dart

@@ -29,7 +29,8 @@ final _router = GoRouter(
     final authState = Provider.of<AuthState>(context, listen: false);
     final bool loggedIn = authState.isLoggedIn;
     final bool loggingIn =
-        state.matchedLocation == '/login' || state.matchedLocation == '/sms_verify';
+        state.matchedLocation == '/login' ||
+        state.matchedLocation == '/sms_verify';
 
     if (!loggedIn && !loggingIn) {
       return '/login';