feat: implement heat map visualization with Leaflet.heat plugin

- Integrate Leaflet.heat plugin for heat map overlay
- Add heat map toggle control in MapFilters component
- Configure heat map intensity based on report quantity levels (minimal: 0.3, moderate: 0.5, significant: 0.7, severe: 1.0)
- Implement heat map layer management with proper cleanup
- Add custom gradient colors (blue to red) for visual intensity representation
- Configure heat map with radius: 25px, blur: 15, maxZoom: 17
- Add TypeScript type declarations for leaflet.heat
- Heat map respects existing filter state (date range, litter type, quantity)

Implements task 5: Create heat map visualization
Requirements: 3.1, 3.5

src/components/map/MapView.tsx

@@ -4,6 +4,7 @@ import 'leaflet/dist/leaflet.css';
 import 'leaflet.markercluster/dist/MarkerCluster.css';
 import 'leaflet.markercluster/dist/MarkerCluster.Default.css';
 import 'leaflet.markercluster';
+import 'leaflet.heat';
 import type { Report, CleanupEvent, FilterState } from '@/types';
 
 // Fix for default marker icons in Leaflet with Vite
@@ -37,6 +38,7 @@ export function MapView({
   onMarkerClick,
   onMapClick,
   showClusters = true,
+  showHeatmap = false,
   center = [53.3498, -6.2603], // Dublin, Ireland default
   zoom = 7,
 }: MapViewProps) {
@@ -44,6 +46,7 @@ export function MapView({
   const mapInstanceRef = useRef<L.Map | null>(null);
   const markersLayerRef = useRef<L.LayerGroup | null>(null);
   const clusterGroupRef = useRef<L.MarkerClusterGroup | null>(null);
+  const heatLayerRef = useRef<L.HeatLayer | null>(null);
 
   // Initialize map
   useEffect(() => {
@@ -99,6 +102,7 @@ export function MapView({
       mapInstanceRef.current = null;
       markersLayerRef.current = null;
       clusterGroupRef.current = null;
+      heatLayerRef.current = null;
     };
   }, []);
 
@@ -221,6 +225,57 @@ export function MapView({
     markersLayer.addTo(map);
   }, [reports, events, filters, showClusters, onMarkerClick]);
 
+  // Update heat map when reports, filters, or showHeatmap changes
+  useEffect(() => {
+    if (!mapInstanceRef.current) return;
+
+    const map = mapInstanceRef.current;
+
+    // Remove existing heat layer if it exists
+    if (heatLayerRef.current && map.hasLayer(heatLayerRef.current)) {
+      map.removeLayer(heatLayerRef.current);
+      heatLayerRef.current = null;
+    }
+
+    // Only create heat layer if showHeatmap is true
+    if (showHeatmap) {
+      const filteredReports = getFilteredReports();
+
+      // Convert reports to heat map data points
+      // Format: [latitude, longitude, intensity]
+      const heatData: [number, number, number][] = filteredReports.map((report) => {
+        // Calculate intensity based on quantity level
+        const intensityMap = {
+          minimal: 0.3,
+          moderate: 0.5,
+          significant: 0.7,
+          severe: 1.0,
+        };
+        const intensity = intensityMap[report.quantity] || 0.5;
+
+        return [report.latitude, report.longitude, intensity];
+      });
+
+      // Create heat layer with configuration
+      if (heatData.length > 0) {
+        heatLayerRef.current = L.heatLayer(heatData, {
+          radius: 25, // Radius of each heat point in pixels
+          blur: 15, // Amount of blur
+          maxZoom: 17, // Maximum zoom level for heat layer
+          max: 1.0, // Maximum intensity value
+          gradient: {
+            0.0: '#0000ff', // Blue for low intensity
+            0.3: '#00ffff', // Cyan
+            0.5: '#00ff00', // Green
+            0.7: '#ffff00', // Yellow
+            0.9: '#ff8800', // Orange
+            1.0: '#ff0000', // Red for high intensity
+          },
+        }).addTo(map);
+      }
+    }
+  }, [reports, filters, showHeatmap]);
+
   // Handle geolocation
   const handleGeolocation = () => {
     if (!navigator.geolocation) {