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.lock

@@ -70,6 +70,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.0.0"
+  flutter_riverpod:
+    dependency: "direct main"
+    description:
+      name: flutter_riverpod
+      sha256: "9532ee6db4a943a1ed8383072a2e3eeda041db5657cdf6d2acecf3c21ecbe7e1"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.6.1"
   flutter_test:
     dependency: "direct dev"
     description: flutter
@@ -139,6 +147,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.9.1"
+  riverpod:
+    dependency: transitive
+    description:
+      name: riverpod
+      sha256: "59062512288d3056b2321804332a13ffdd1bf16df70dcc8e506e411280a72959"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.6.1"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -160,6 +176,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.12.1"
+  state_notifier:
+    dependency: transitive
+    description:
+      name: state_notifier
+      sha256: b8677376aa54f2d7c58280d5a007f9e8774f1968d1fb1c096adcb4792fba29bb
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.0.0"
   stream_channel:
     dependency: transitive
     description: