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/home/home_screen.dart

@@ -52,7 +52,9 @@ class _LoggedInView extends StatelessWidget {
                   child: ListTile(
                     leading: const Icon(Icons.person),
                     title: Text(authState.currentUser!.displayName ?? 'User'),
-                    subtitle: Text(authState.currentUser!.phoneNumber ?? 'No phone number'),
+                    subtitle: Text(
+                      authState.currentUser!.phoneNumber ?? 'No phone number',
+                    ),
                   ),
                 ),
                 const Divider(),