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

src/types/index.ts

@@ -149,12 +149,14 @@ export interface AnalyticsSummary {
   totalReports: number;
   totalEvents: number;
   totalUsers: number;
-  totalLitterCollected?: number; // in kilograms
-  periodComparison?: {
-    reports: number; // percentage change
-    events: number;
-    users: number;
-  };
+  totalLitterCollected: number; // in kilograms
+  reportsByType: Record<string, number>;
+  reportsByQuantity: Record<string, number>;
+  verifiedReports: number;
+  cleanedReports: number;
+  activeUsers: number;
+  upcomingEvents: number;
+  completedEvents: number;
 }
 
 export interface DateRange {
@@ -164,20 +166,19 @@ export interface DateRange {
 
 export interface TimeSeriesDataPoint {
   date: string;
-  reports: number;
-  events?: number;
+  reportCount: number;
+  eventCount: number;
+  litterCollected: number;
 }
 
 export interface LitterTypeDistribution {
-  type: LitterType;
+  type: string;
   count: number;
-  percentage: number;
 }
 
 export interface QuantityAggregation {
-  quantity: QuantityLevel;
+  level: string;
   count: number;
-  percentage: number;
 }
 
 // External environmental data types