Implement complete GPS speedometer functionality

Features implemented:
- Real-time GPS speed tracking with permission handling
- Customizable speed units (km/h, mph) with persistent settings
- Digital and analog speedometer display styles
- Dark/light theme support with system integration
- Optional metrics: coordinates, distance, trip time, GPS accuracy
- Trip reset functionality and error handling
- Modular architecture with Provider state management

Technical details:
- Added dependencies: geolocator, permission_handler, provider, shared_preferences
- Configured Android location permissions (FINE_LOCATION, COARSE_LOCATION)
- Portrait orientation lock for mobile-first experience
- Extensible settings system for future customization options
- Clean separation of concerns: providers, screens, widgets

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

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

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