feat: implement analytics endpoints (task 28)

- Created analytics service with summary, trends, comparison, and aggregated data methods
- Implemented 5 analytics endpoints: summary, trends, comparison, aggregated, and CSV export
- Added time series data with day/week/month interval support
- Implemented period-over-period comparison metrics with percentage changes
- Added CSV export functionality using json2csv
- Updated frontend analytics service to unwrap API responses
- Fixed chart components to work with new data structure (reportCount, eventCount, litterCollected)
- Updated TypeScript types to match backend API structure
- All endpoints tested and verified working

Requirements satisfied: 5.1, 5.2, 5.3, 5.4, 5.5

server/src/routes/analyticsRoutes.ts

@@ -0,0 +1,13 @@
+import { Router } from 'express';
+import { analyticsController } from '../controllers/analyticsController';
+
+const router = Router();
+
+// Analytics endpoints
+router.get('/summary', analyticsController.getSummary.bind(analyticsController));
+router.get('/trends', analyticsController.getTrends.bind(analyticsController));
+router.get('/comparison', analyticsController.getComparison.bind(analyticsController));
+router.get('/export', analyticsController.exportCSV.bind(analyticsController));
+router.get('/aggregated', analyticsController.getAggregatedData.bind(analyticsController));
+
+export default router;