fix: map view freezing browser with thousands of markers

Replace DivIcon thumbnail markers with lightweight CircleMarkers.
Each DivIcon created a DOM element with an <img> tag, so 3K+
geotagged photos meant 3K DOM nodes and 3K thumbnail requests
hitting simultaneously — freezing the browser during clustering.

CircleMarkers are SVG-rendered on Leaflet's canvas layer with no
DOM nodes per marker. Photos still open in preview on click.

Also: bump cluster radius 50→80, enable removeOutsideVisibleBounds,
disable clustering at max zoom, increase staleTime to 5 min.

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

frontend/src/components/map/MapView.tsx

@@ -1,9 +1,6 @@
 import { useEffect, useMemo, useRef } from 'react'
 import { useQuery } from '@tanstack/react-query'
-import { MapContainer, TileLayer, Marker, useMap } from 'react-leaflet'
-// react-leaflet-cluster has no own .d.ts that survives strict mode in
-// every project, so we let TS infer from its runtime export.
-// eslint-disable-next-line @typescript-eslint/ban-ts-comment
+import { MapContainer, TileLayer, CircleMarker, useMap } from 'react-leaflet'
 // @ts-ignore — package ships JS with no bundled types
 import MarkerClusterGroup from 'react-leaflet-cluster'
 import L from 'leaflet'
@@ -18,24 +15,8 @@ interface MapPoint {
   taken_at: string | null
 }
 
-/** Build the divIcon used for each photo marker. The HTML is a tiny
- *  square thumbnail with a white border + drop shadow so it reads on
- *  any tile background. Memoised per-photo so we don't re-create the
- *  L.DivIcon on every re-render. */
-function buildPhotoIcon(photoId: string): L.DivIcon {
-  const url = photosApi.getThumbnailUrl(photoId, 'small')
-  return L.divIcon({
-    className: 'photo-map-marker',
-    html: `<div class="pmm-frame"><img src="${url}" loading="lazy" alt="" /></div>`,
-    iconSize: [56, 56],
-    iconAnchor: [28, 28],
-    popupAnchor: [0, -28],
-  })
-}
-
 /** Pans/zooms the map to fit the supplied points the first time they
- *  arrive. Subsequent loads (e.g. cache refresh) leave the user's pan
- *  alone — they're probably mid-investigation. */
+ *  arrive. Subsequent loads leave the user's pan alone. */
 function FitBoundsOnce({ points }: { points: MapPoint[] }) {
   const map = useMap()
   const fittedRef = useRef(false)
@@ -52,25 +33,10 @@ export function MapView() {
   const { data: points = [], isLoading, error } = useQuery({
     queryKey: ['photos', 'map'],
     queryFn: () => photosApi.mapPoints(),
-    staleTime: 60 * 1000,
+    staleTime: 5 * 60 * 1000,
   })
 
-  // Marker click hands off to the same PreviewView the timeline uses, so
-  // the user gets the full preview UI (large image, info panel with
-  // location, filmstrip nav between map photos) instead of a bespoke
-  // map-only lightbox. We pass the map's own point order as the visible
-  // sequence so left/right arrows step through neighboring markers.
   const openPreview = usePhotoStore((s) => s.openPreview)
-
-  // Stable per-marker icons. Re-created only when the set of point ids
-  // changes — the underlying L.DivIcon objects are pure HTML so reusing
-  // them is safe across re-renders.
-  const iconsById = useMemo(() => {
-    const map = new Map<string, L.DivIcon>()
-    for (const p of points) map.set(p.id, buildPhotoIcon(p.id))
-    return map
-  }, [points])
-
   const visibleSequence = useMemo(() => points.map((p) => p.id), [points])
 
   if (isLoading) {
@@ -116,54 +82,33 @@ export function MapView() {
           url="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
         />
         <FitBoundsOnce points={points} />
-        <MarkerClusterGroup chunkedLoading maxClusterRadius={50}>
-          {points.map((p) => {
-            const icon = iconsById.get(p.id)
-            if (!icon) return null
-            return (
-              <PhotoMarker
+        <MarkerClusterGroup
+          chunkedLoading
+          maxClusterRadius={80}
+          disableClusteringAtZoom={18}
+          spiderfyOnMaxZoom={false}
+          showCoverageOnHover={false}
+          removeOutsideVisibleBounds
+        >
+          {points.map((p) => (
+            <CircleMarker
               key={p.id}
-                point={p}
-                icon={icon}
-                onClick={() => openPreview(p.id, visibleSequence)}
+              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>
       </MapContainer>
-
-      <style>{`
-        .photo-map-marker { background: transparent; border: none; }
-        .photo-map-marker .pmm-frame {
-          width: 56px; height: 56px;
-          border-radius: 8px;
-          overflow: hidden;
-          border: 2px solid white;
-          box-shadow: 0 2px 6px rgba(0,0,0,0.4);
-          background: #1f2937;
-        }
-        .photo-map-marker .pmm-frame img {
-          width: 100%; height: 100%; object-fit: cover; display: block;
-        }
-      `}</style>
     </div>
   )
 }
-
-function PhotoMarker({
-  point,
-  icon,
-  onClick,
-}: {
-  point: MapPoint
-  icon: L.DivIcon
-  onClick: () => void
-}) {
-  return (
-    <Marker
-      position={[point.latitude, point.longitude]}
-      icon={icon}
-      eventHandlers={{ click: onClick }}
-    />
-  )
-}