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/services/analyticsService.ts

@@ -15,13 +15,38 @@ class AnalyticsService {
     }
 
     const queryString = params.toString();
-    return apiClient.get<AnalyticsSummary>(`/analytics/summary${queryString ? `?${queryString}` : ''}`);
+    const response = await apiClient.get<{ success: boolean; data: AnalyticsSummary }>(`/analytics/summary${queryString ? `?${queryString}` : ''}`);
+    return response.data;
   }
 
   /**
    * Get time series data for report trends
    */
-  async getTimeSeries(dateRange?: { start: string; end: string }): Promise<TimeSeriesDataPoint[]> {
+  async getTimeSeries(
+    dateRange?: { start: string; end: string },
+    interval: 'day' | 'week' | 'month' = 'day'
+  ): Promise<TimeSeriesDataPoint[]> {
+    const params = new URLSearchParams();
+    
+    if (dateRange) {
+      params.append('startDate', dateRange.start);
+      params.append('endDate', dateRange.end);
+    }
+    params.append('interval', interval);
+
+    const queryString = params.toString();
+    const response = await apiClient.get<{ success: boolean; data: TimeSeriesDataPoint[] }>(`/analytics/trends${queryString ? `?${queryString}` : ''}`);
+    return response.data;
+  }
+
+  /**
+   * Get aggregated data (litter types, quantities, verification status)
+   */
+  async getAggregatedData(dateRange?: { start: string; end: string }): Promise<{
+    litterTypes: LitterTypeDistribution[];
+    quantities: QuantityAggregation[];
+    verificationStatus: Array<{ status: string; count: number }>;
+  }> {
     const params = new URLSearchParams();
     
     if (dateRange) {
@@ -30,37 +55,56 @@ class AnalyticsService {
     }
 
     const queryString = params.toString();
-    return apiClient.get<TimeSeriesDataPoint[]>(`/analytics/trends${queryString ? `?${queryString}` : ''}`);
+    const response = await apiClient.get<{ success: boolean; data: {
+      litterTypes: LitterTypeDistribution[];
+      quantities: QuantityAggregation[];
+      verificationStatus: Array<{ status: string; count: number }>;
+    } }>(`/analytics/aggregated${queryString ? `?${queryString}` : ''}`);
+    return response.data;
   }
 
   /**
    * Get litter type distribution data
    */
   async getLitterTypeDistribution(dateRange?: { start: string; end: string }): Promise<LitterTypeDistribution[]> {
-    const params = new URLSearchParams();
-    
-    if (dateRange) {
-      params.append('startDate', dateRange.start);
-      params.append('endDate', dateRange.end);
-    }
-
-    const queryString = params.toString();
-    return apiClient.get<LitterTypeDistribution[]>(`/analytics/litter-types${queryString ? `?${queryString}` : ''}`);
+    const data = await this.getAggregatedData(dateRange);
+    return data.litterTypes;
   }
 
   /**
    * Get quantity estimation aggregation data
    */
   async getQuantityAggregation(dateRange?: { start: string; end: string }): Promise<QuantityAggregation[]> {
-    const params = new URLSearchParams();
-    
-    if (dateRange) {
-      params.append('startDate', dateRange.start);
-      params.append('endDate', dateRange.end);
-    }
+    const data = await this.getAggregatedData(dateRange);
+    return data.quantities;
+  }
 
-    const queryString = params.toString();
-    return apiClient.get<QuantityAggregation[]>(`/analytics/quantities${queryString ? `?${queryString}` : ''}`);
+  /**
+   * Get comparison metrics for period-over-period analysis
+   */
+  async getComparisonMetrics(
+    currentStart: string,
+    currentEnd: string,
+    previousStart: string,
+    previousEnd: string
+  ): Promise<{
+    current: { reports: number; events: number; users: number };
+    previous: { reports: number; events: number; users: number };
+    percentageChange: { reports: number; events: number; users: number };
+  }> {
+    const params = new URLSearchParams({
+      currentStart,
+      currentEnd,
+      previousStart,
+      previousEnd,
+    });
+
+    const response = await apiClient.get<{ success: boolean; data: {
+      current: { reports: number; events: number; users: number };
+      previous: { reports: number; events: number; users: number };
+      percentageChange: { reports: number; events: number; users: number };
+    } }>(`/analytics/comparison?${params.toString()}`);
+    return response.data;
   }
 
   /**