feat: implement data visualization charts for analytics dashboard

- Add TimeSeriesChart component for report trends over time
- Add LitterTypeChart component with pie chart for type distribution
- Add QuantityChart component with bar chart for quantity aggregation
- Update analytics service with new API methods for chart data
- Add new types for chart data structures (TimeSeriesDataPoint, LitterTypeDistribution, QuantityAggregation)
- Integrate charts into AnalyticsPage with responsive grid layout
- Add mock data fallback for development when API is not available
- Configure charts for mobile responsiveness
- Implement comparison metrics display in time series
- Add loading states and empty states for all charts

Implements task 11: Data visualization charts
Requirements: 5.2, 5.3, 5.4

.kiro/specs/beach-litter-mapping/tasks.md

@@ -83,7 +83,7 @@
   - Create export to CSV functionality
   - _Requirements: 5.1, 5.5_
 
-- [ ] 11. Implement data visualization charts
+- [x] 11. Implement data visualization charts
   - Create time series chart for report trends
   - Build pie chart for litter type distribution
   - Implement comparison metrics with previous periods