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

src/components/analytics/index.ts

@@ -1,2 +1,5 @@
 export { DateRangeSelector } from './DateRangeSelector';
 export { StatCard } from './StatCard';
+export { TimeSeriesChart } from './TimeSeriesChart';
+export { LitterTypeChart } from './LitterTypeChart';
+export { QuantityChart } from './QuantityChart';