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/auth/sms_verification_screen.dart

@@ -78,12 +78,17 @@ class _SmsVerificationScreenState extends State<SmsVerificationScreen> {
                         ? () async {
                             // In a real app, we'd have the verificationId from the previous step
                             if (_verificationId != null) {
-                              await authState.verifyOTP(_verificationId!, _pinController.text);
+                              await authState.verifyOTP(
+                                _verificationId!,
+                                _pinController.text,
+                              );
                               if (!context.mounted) return;
 
                               if (authState.errorMessage != null) {
                                 ScaffoldMessenger.of(context).showSnackBar(
-                                  SnackBar(content: Text(authState.errorMessage!)),
+                                  SnackBar(
+                                    content: Text(authState.errorMessage!),
+                                  ),
                                 );
                               } else {
                                 context.go('/');