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/types/index.ts

@@ -137,3 +137,21 @@ export interface DateRange {
   start: Date;
   end: Date;
 }
+
+export interface TimeSeriesDataPoint {
+  date: string;
+  reports: number;
+  events?: number;
+}
+
+export interface LitterTypeDistribution {
+  type: LitterType;
+  count: number;
+  percentage: number;
+}
+
+export interface QuantityAggregation {
+  quantity: QuantityLevel;
+  count: number;
+  percentage: number;
+}