chore: upgrade to riverpod 3.x and freezed 3.x

- Upgrade flutter_riverpod to 3.1.0, riverpod_annotation to 4.0.0
- Upgrade freezed to 3.2.3, freezed_annotation to 3.1.0
- Migrate freezed classes to use sealed keyword (freezed 3.x)
- Update provider naming (*NotifierProvider → *Provider)
- Add legacy.dart import for StateNotifierProvider compatibility
- Fix valueOrNull → value for AsyncValue
- Remove unused imports and fields
- Add sync from Authentik button to users/groups pages
- Suppress invalid_annotation_target warning in analysis_options

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pubspec.yaml

@@ -32,20 +32,20 @@ dependencies:
     sdk: flutter
 
   # State Management
-  flutter_riverpod: ^2.6.1
-  riverpod_annotation: ^2.6.1
-  hooks_riverpod: ^2.6.1
-  flutter_hooks: ^0.20.5
+  flutter_riverpod: ^3.0.0
+  riverpod_annotation: ^4.0.0
+  hooks_riverpod: ^3.0.0
+  flutter_hooks: ^0.21.0
 
   # Code Generation Support
-  freezed_annotation: ^2.4.4
+  freezed_annotation: ^3.1.0
   json_annotation: ^4.9.0
 
   # Networking
   dio: ^5.7.0
 
   # Routing
-  go_router: ^14.6.2
+  go_router: ^17.0.1
 
   # Storage
   shared_preferences: ^2.3.3
@@ -54,7 +54,7 @@ dependencies:
   flex_color_scheme: ^8.1.0
   flutter_adaptive_scaffold: ^0.3.1
   flutter_markdown: ^0.7.4
-  fl_chart: ^0.69.2
+  fl_chart: ^1.1.1
 
   # Icons
   cupertino_icons: ^1.0.8
@@ -70,19 +70,19 @@ dev_dependencies:
     sdk: flutter
 
   # Linting
-  flutter_lints: ^5.0.0
+  flutter_lints: ^6.0.0
 
   # Code Generation
   build_runner: ^2.4.13
-  freezed: ^2.5.7
+  freezed: ^3.2.3
   json_serializable: ^6.8.0
-  riverpod_generator: ^2.6.3
+  riverpod_generator: ^4.0.0
 
   # Testing
   mocktail: ^1.0.4
 
   # Build tools
-  build: ^2.4.0
+  build: ^4.0.3
   yaml: ^3.1.0
 
 # For information on the generic Dart part of this file, see the