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)

lib/features/recycling_guide/presentation/providers/recycling_provider.dart

@@ -45,20 +45,20 @@ final recyclingSearchProvider =
 sealed class RecyclingSearchState {
   const RecyclingSearchState();
 
-  const factory RecyclingSearchState.idle() = _Idle;
-  const factory RecyclingSearchState.loading() = _Loading;
-  const factory RecyclingSearchState.done(List<SearchResult> results) = _Done;
+  const factory RecyclingSearchState.idle() = Idle;
+  const factory RecyclingSearchState.loading() = Loading;
+  const factory RecyclingSearchState.done(List<SearchResult> results) = Done;
 }
 
-class _Idle extends RecyclingSearchState {
-  const _Idle();
+class Idle extends RecyclingSearchState {
+  const Idle();
 }
 
-class _Loading extends RecyclingSearchState {
-  const _Loading();
+class Loading extends RecyclingSearchState {
+  const Loading();
 }
 
-class _Done extends RecyclingSearchState {
+class Done extends RecyclingSearchState {
   final List<SearchResult> results;
-  const _Done(this.results);
+  const Done(this.results);
 }