feat: add flutter-dev skill

Add comprehensive Flutter cross-platform development guide covering:
- Widget patterns and const optimization
- Riverpod/Bloc state management
- GoRouter navigation
- Performance optimization
- Testing strategies
- Platform-specific implementations

Made-with: Cursor

skills/flutter-dev/SKILL.md

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+---
+name: flutter-dev
+description: |
+  Flutter cross-platform development guide covering widget patterns, Riverpod/Bloc state management, GoRouter navigation, performance optimization, and platform-specific implementations. Includes const optimization, responsive layouts, testing strategies, and DevTools profiling.
+  Use when: building Flutter apps, implementing state management (Riverpod/Bloc), setting up GoRouter navigation, creating custom widgets, optimizing performance, writing widget tests, cross-platform development.
+license: MIT
+metadata:
+  version: "1.0.0"
+  category: mobile
+  sources:
+    - Flutter Documentation
+    - Riverpod Documentation
+    - Bloc Library Documentation
+---
+
+# Flutter Development Guide
+
+A practical guide for building cross-platform applications with Flutter 3 and Dart. Focuses on proven patterns, state management, and performance optimization.
+
+## Quick Reference
+
+### Widget Patterns
+
+| Purpose | Component |
+|---------|-----------|
+| State management (simple) | `StateProvider` + `ConsumerWidget` |
+| State management (complex) | `NotifierProvider` / `Bloc` |
+| Async data | `FutureProvider` / `AsyncNotifierProvider` |
+| Real-time streams | `StreamProvider` |
+| Navigation | `GoRouter` + `context.go/push` |
+| Responsive layout | `LayoutBuilder` + breakpoints |
+| List display | `ListView.builder` |
+| Complex scrolling | `CustomScrollView` + Slivers |
+| Hooks | `HookWidget` + `useState/useEffect` |
+| Forms | `Form` + `TextFormField` + validation |
+
+### Performance Patterns
+
+| Purpose | Solution |
+|---------|----------|
+| Prevent rebuilds | `const` constructors |
+| Selective updates | `ref.watch(provider.select(...))` |
+| Isolate repaints | `RepaintBoundary` |
+| Lazy lists | `ListView.builder` |
+| Heavy computation | `compute()` isolate |
+| Image caching | `cached_network_image` |
+
+## Core Principles
+
+### Widget Optimization
+- Use `const` constructors wherever possible
+- Extract static widgets to separate const classes
+- Use `Key` for list items (ValueKey, ObjectKey)
+- Prefer `ConsumerWidget` over `StatefulWidget` for state
+
+### State Management
+- Riverpod for dependency injection and simple state
+- Bloc/Cubit for event-driven workflows and complex logic
+- Never mutate state directly (create new instances)
+- Use `select()` to minimize rebuilds
+
+### Layout
+- 8pt spacing increments (8, 16, 24, 32, 48)
+- Responsive breakpoints: mobile (<650), tablet (650-1100), desktop (>1100)
+- Support all screen sizes with flexible layouts
+- Follow Material 3 / Cupertino design guidelines
+
+### Performance
+- Profile with DevTools before optimizing
+- Target <16ms frame time for 60fps
+- Use `RepaintBoundary` for complex animations
+- Offload heavy work with `compute()`
+
+## Checklist
+
+### Widget Best Practices
+- [ ] `const` constructors on all static widgets
+- [ ] Proper `Key` on list items
+- [ ] `ConsumerWidget` for state-dependent widgets
+- [ ] No widget building inside `build()` method
+- [ ] Extract reusable widgets to separate files
+
+### State Management
+- [ ] Immutable state objects
+- [ ] `select()` for granular rebuilds
+- [ ] Proper provider scoping
+- [ ] Dispose controllers and subscriptions
+- [ ] Handle loading/error states
+
+### Navigation
+- [ ] GoRouter with typed routes
+- [ ] Auth guards via redirect
+- [ ] Deep linking support
+- [ ] State preservation across routes
+
+### Performance
+- [ ] Profile mode testing (`flutter run --profile`)
+- [ ] <16ms frame rendering time
+- [ ] No unnecessary rebuilds (DevTools check)
+- [ ] Images cached and resized
+- [ ] Heavy computation in isolates
+
+### Testing
+- [ ] Widget tests for UI components
+- [ ] Unit tests for business logic
+- [ ] Integration tests for user flows
+- [ ] Bloc tests with `blocTest()`
+
+## References
+
+| Topic | Reference |
+|-------|-----------|
+| Widget patterns, const optimization, responsive layout | [Widget Patterns](references/widget-patterns.md) |
+| Riverpod providers, notifiers, async state | [Riverpod State Management](references/riverpod-state.md) |
+| Bloc, Cubit, event-driven state | [Bloc State Management](references/bloc-state.md) |
+| GoRouter setup, routes, deep linking | [GoRouter Navigation](references/gorouter-navigation.md) |
+| Feature-based structure, dependencies | [Project Structure](references/project-structure.md) |
+| Profiling, const optimization, DevTools | [Performance Optimization](references/performance.md) |
+| Widget tests, integration tests, mocking | [Testing Strategies](references/testing.md) |
+| iOS/Android/Web specific implementations | [Platform Integration](references/platform-specific.md) |
+| Implicit/explicit animations, Hero, transitions | [Animations](references/animations.md) |
+| Dio, interceptors, error handling, caching | [Networking](references/networking.md) |
+| Form validation, FormField, input formatters | [Forms](references/forms.md) |
+| i18n, flutter_localizations, intl | [Localization](references/localization.md) |
+
+---
+
+Flutter, Dart, Material Design, and Cupertino are trademarks of Google LLC and Apple Inc. respectively. Riverpod, Bloc, and GoRouter are open-source packages by their respective maintainers.