feat: implement hotspot visualization on map

- Add HotspotSeverity type and HotspotWithSeverity interface
- Implement getHotspots() method in analyticsService with severity calculation
- Add hotspot layer to MapView component with color-coded circles
- Create hotspot markers with severity icons and report count badges
- Add detailed hotspot popups showing report count, severity score, radius, and dates
- Implement hotspot toggle control in MapFilters with loading state
- Add hotspot severity legend to MapFilters
- Integrate hotspot data fetching in MapPage with sample fallback data
- Color-code hotspot boundaries: yellow (low), orange (medium/high), red (critical)
- Display hotspot statistics in interactive popups

Implements task 12: Create hotspot visualization
Requirements: 3.2, 3.3, 3.5

src/types/index.ts

@@ -83,6 +83,12 @@ export interface Hotspot {
   calculatedAt: Date;
 }
 
+export type HotspotSeverity = 'low' | 'medium' | 'high' | 'critical';
+
+export interface HotspotWithSeverity extends Hotspot {
+  severity: HotspotSeverity;
+}
+
 // DTOs (Data Transfer Objects)
 export interface CreateReportDTO {
   photos: File[];