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/screens/recycling_guide_screen.dart

@@ -137,10 +137,13 @@ class _SearchResults extends ConsumerWidget {
   Widget build(BuildContext context, WidgetRef ref) {
     final estado = ref.watch(recyclingSearchProvider);
 
-    return switch (estado) {
-      _Idle()    => const SizedBox.shrink(),
-      _Loading() => const Center(child: CircularProgressIndicator()),
-      _Done(results: final r) when r.isEmpty => Center(
+    if (estado is Idle) {
+      return const SizedBox.shrink();
+    } else if (estado is Loading) {
+      return const Center(child: CircularProgressIndicator());
+    } else if (estado is Done) {
+      if (estado.results.isEmpty) {
+        return Center(
           child: Column(
             mainAxisSize: MainAxisSize.min,
             children: [
@@ -152,13 +155,14 @@ class _SearchResults extends ConsumerWidget {
               ),
             ],
           ),
-        ),
-      _Done(results: final r) => ListView.builder(
-          padding: const EdgeInsets.symmetric(vertical: 8),
-          itemCount: r.length,
-          itemBuilder: (_, i) => SearchResultTile(resultado: r[i]),
-        ),
-      _ => const SizedBox.shrink(),
-    };
+        );
+      }
+      return ListView.builder(
+        padding: const EdgeInsets.symmetric(vertical: 8),
+        itemCount: estado.results.length,
+        itemBuilder: (_, i) => SearchResultTile(resultado: estado.results[i]),
+      );
+    }
+    return const SizedBox.shrink();
   }
 }