feat: implement statistics visualization system

Features:
- Daily/Weekly/Monthly statistics views
- Activity heatmap
- Interruption tracking and analysis
- Historical data visualization
- Statistics drawer integration

Files:
- New components: Stats-day, Stats-week, Stats-month, Stats-heatmap
- New utilities: StatisticsAnalyzer, StatisticsStore
- Updated Timer with interruption dialog
- Documentation: STATISTICS_FEATURE.md, STATISTICS_QUICKSTART.md

feat: implement statistics visualization system

Features:
- Daily/Weekly/Monthly statistics views
- Activity heatmap
- Interruption tracking and analysis
- Historical data visualization
- Statistics drawer integration

Files:
- New components: Stats-day, Stats-week, Stats-month, Stats-heatmap
- New utilities: StatisticsAnalyzer, StatisticsStore
- Updated Timer with interruption dialog
- Documentation: STATISTICS_FEATURE.md, STATISTICS_QUICKSTART.md