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/phone_input_screen.dart

@@ -13,7 +13,6 @@ class PhoneInputScreen extends StatefulWidget {
 
 class _PhoneInputScreenState extends State<PhoneInputScreen> {
   final TextEditingController _phoneController = TextEditingController();
-  String? _selectedCountry;
   String? _formattedPhone;
 
   @override
@@ -42,9 +41,6 @@ class _PhoneInputScreenState extends State<PhoneInputScreen> {
               onChanged: (phone) {
                 _formattedPhone = phone.completeNumber;
               },
-              onCountryChanged: (country) {
-                _selectedCountry = country.isoCode;
-              },
             ),
             const SizedBox(height: 20),
             authState.isLoading
@@ -53,12 +49,16 @@ class _PhoneInputScreenState extends State<PhoneInputScreen> {
                     onPressed: _formattedPhone != null
                         ? () async {
                             if (_formattedPhone != null) {
-                              await authState.signInWithPhoneNumber(_formattedPhone!);
+                              await authState.signInWithPhoneNumber(
+                                _formattedPhone!,
+                              );
                               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('/sms_verify');