fix: resolve compilation errors

- Add flutter_riverpod dependency to pubspec.yaml
- Rename sealed class subtypes (Idle, Loading, Done) as public
- Update RecyclingGuideScreen to use type checks instead of pattern matching
- Fix CardThemeData type in app_theme.dart
- Keep withOpacity (warnings only, not errors)

pubspec.yaml

@@ -34,6 +34,7 @@ dependencies:
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
   cupertino_icons: ^1.0.8
+  flutter_riverpod: ^2.4.0
 
 dev_dependencies:
   flutter_test: