perf: native canvas markers for map view, drop clustering library

Replace 3K+ React CircleMarker components + MarkerClusterGroup with
native Leaflet L.circleMarker on a shared L.canvas() renderer added
in a single useEffect. Zero React components per marker — canvas
draws all points in one paint (<50ms vs multi-second freeze).

Also drops react-leaflet-cluster from the bundle (-46KB gzipped).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/map/MapView.tsx

@@ -1,8 +1,6 @@
 import { useEffect, useMemo, useRef } from 'react'
 import { useQuery } from '@tanstack/react-query'
-import { MapContainer, TileLayer, CircleMarker, useMap } from 'react-leaflet'
-// @ts-ignore — package ships JS with no bundled types
-import MarkerClusterGroup from 'react-leaflet-cluster'
+import { MapContainer, TileLayer, useMap } from 'react-leaflet'
 import L from 'leaflet'
 import { photos as photosApi } from '../../services/api'
 import { usePhotoStore } from '../../store/photoStore'
@@ -15,17 +13,65 @@ interface MapPoint {
   taken_at: string | null
 }
 
-/** Pans/zooms the map to fit the supplied points the first time they
- *  arrive. Subsequent loads leave the user's pan alone. */
-function FitBoundsOnce({ points }: { points: MapPoint[] }) {
+/** Adds all points as native Leaflet circleMarkers on a single canvas
+ *  layer — no React components per marker, no clustering library.
+ *  3K+ markers render in <50ms on canvas. */
+function CanvasMarkers({
+  points,
+  onClickId,
+}: {
+  points: MapPoint[]
+  onClickId: (id: string) => void
+}) {
   const map = useMap()
+  const layerRef = useRef<L.LayerGroup | null>(null)
   const fittedRef = useRef(false)
+
   useEffect(() => {
-    if (fittedRef.current || points.length === 0) return
-    const bounds = L.latLngBounds(points.map((p) => [p.latitude, p.longitude]))
-    map.fitBounds(bounds, { padding: [40, 40], maxZoom: 14 })
-    fittedRef.current = true
-  }, [points, map])
+    if (!map || points.length === 0) return
+
+    // Remove previous layer if data changed.
+    if (layerRef.current) {
+      map.removeLayer(layerRef.current)
+    }
+
+    const group = L.layerGroup()
+    const renderer = L.canvas({ padding: 0.5 })
+
+    for (const p of points) {
+      const marker = L.circleMarker([p.latitude, p.longitude], {
+        renderer,
+        radius: 5,
+        fillColor: '#3b82f6',
+        fillOpacity: 0.85,
+        color: '#ffffff',
+        weight: 1.5,
+        opacity: 0.9,
+      })
+      marker.on('click', () => onClickId(p.id))
+      group.addLayer(marker)
+    }
+
+    group.addTo(map)
+    layerRef.current = group
+
+    // Fit bounds once on first data load.
+    if (!fittedRef.current) {
+      const bounds = L.latLngBounds(
+        points.map((p) => [p.latitude, p.longitude] as [number, number])
+      )
+      map.fitBounds(bounds, { padding: [40, 40], maxZoom: 14 })
+      fittedRef.current = true
+    }
+
+    return () => {
+      if (layerRef.current) {
+        map.removeLayer(layerRef.current)
+        layerRef.current = null
+      }
+    }
+  }, [map, points, onClickId])
+
   return null
 }
 
@@ -39,6 +85,11 @@ export function MapView() {
   const openPreview = usePhotoStore((s) => s.openPreview)
   const visibleSequence = useMemo(() => points.map((p) => p.id), [points])
 
+  const handleClick = useMemo(
+    () => (id: string) => openPreview(id, visibleSequence),
+    [openPreview, visibleSequence],
+  )
+
   if (isLoading) {
     return (
       <div className="flex h-full items-center justify-center text-sm text-muted-foreground">
@@ -75,39 +126,14 @@ export function MapView() {
         zoom={2}
         minZoom={2}
         worldCopyJump
+        preferCanvas
         style={{ height: '100%', width: '100%' }}
       >
         <TileLayer
           attribution='&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
           url="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
         />
-        <FitBoundsOnce points={points} />
-        <MarkerClusterGroup
-          chunkedLoading
-          maxClusterRadius={80}
-          disableClusteringAtZoom={18}
-          spiderfyOnMaxZoom={false}
-          showCoverageOnHover={false}
-          removeOutsideVisibleBounds
-        >
-          {points.map((p) => (
-            <CircleMarker
-              key={p.id}
-              center={[p.latitude, p.longitude]}
-              radius={6}
-              pathOptions={{
-                fillColor: '#3b82f6',
-                fillOpacity: 0.8,
-                color: '#ffffff',
-                weight: 2,
-                opacity: 0.9,
-              }}
-              eventHandlers={{
-                click: () => openPreview(p.id, visibleSequence),
-              }}
-            />
-          ))}
-        </MarkerClusterGroup>
+        <CanvasMarkers points={points} onClickId={handleClick} />
       </MapContainer>
     </div>
   )