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 <[email protected]>

.claude/settings.local.json

@@ -2,7 +2,11 @@
   "permissions": {
     "allow": [
       "Bash(code .:*)",
-      "Bash(git add:*)"
+      "Bash(git add:*)",
+      "Bash(git commit:*)",
+      "Bash(flutter analyze:*)",
+      "Bash(flutter format:*)",
+      "Bash(dart format:*)"
     ]
   }
 }