- Add ScreenCastComponent: New threaded component for screen capture and streaming
- Implement FFmpeg-based cross-platform screen capture (Linux, Windows, macOS)
- Add Chromecast device discovery and streaming using pychromecast
- Create web-based screen cast interface at /screen_cast with real-time controls
- Add HTTP streaming server for Chromecast-compatible video delivery
- Integrate screen cast settings into web dashboard configuration panel
- Add --no-screen-cast command line flag (enabled by default)
- Update dependencies: ffmpeg-python>=0.2.0, pychromecast>=13.0.0

New Files:
- mbetterclient/core/screen_cast.py: Main ScreenCastComponent implementation
- mbetterclient/web_dashboard/screen_cast_routes.py: Flask API routes
- mbetterclient/web_dashboard/templates/dashboard/screen_cast.html: Web interface
- test_screen_cast_integration.py: Integration test suite

Key Features:
- Real-time device discovery and status updates
- Platform-specific audio/video input sources
- Quality settings (resolution, frame rate, bitrate)
- Network stream URL generation for Chromecast access
- Proper component lifecycle management and cleanup
- Message bus integration with WEB_ACTION support

Documentation:
- Updated README.md with screen casting features and usage
- Added comprehensive CHANGELOG.md entry for v1.2.4
- Extended DOCUMENTATION.md with complete screen casting guide

Architecture Enhancement:
- Extended from 4 to 5 threaded components
- Added ScreenCastConfig to settings with database persistence
- Enhanced web dashboard navigation with screen cast section