Fix marker stability and reduce image preview size

- Use deterministic hash-based offset calculation for stable marker positions
- Markers now stay in same position across zoom/pan operations
- Check geographic distance instead of pixel distance for clustering
- Reduce image preview from 60px to 40px for compact modal
- Reduce button font size to save space

Fixes: Markers no longer jump around when zooming
Fixes: Modal stays compact with image preview

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/components/Map/MapView.jsx

@@ -608,7 +608,7 @@ export default function MapView({
                     <img
                       src={draftImagePreview}
                       alt="Preview"
-                      style={{ width: "60px", height: "60px", objectFit: "cover", borderRadius: "8px" }}
+                      style={{ width: "40px", height: "40px", objectFit: "cover", borderRadius: "6px" }}
                     />
                     <button
                       type="button"
@@ -617,7 +617,7 @@ export default function MapView({
                         setDraftImagePreview("");
                         setDraftImage("");
                       }}
-                      style={{ padding: "4px 8px", fontSize: "12px" }}
+                      style={{ padding: "4px 8px", fontSize: "11px" }}
                     >
                       Remove
                     </button>

src/components/Map/markerManager.js

@@ -294,6 +294,18 @@ function openCenteredOverlay({ map, post, theme }) {
   };
 }
 
+function hashPostId(id) {
+  // Simple hash function for stable offset calculation
+  const str = String(id);
+  let hash = 0;
+  for (let i = 0; i < str.length; i++) {
+    const char = str.charCodeAt(i);
+    hash = ((hash << 5) - hash) + char;
+    hash = hash & hash; // Convert to 32bit integer
+  }
+  return Math.abs(hash);
+}
+
 function calculateSmartOffset(post, markersRef, map) {
   if (!map || !markersRef.current) return { x: 0, y: 0 };
 
@@ -302,35 +314,31 @@ function calculateSmartOffset(post, markersRef, map) {
   if (lat == null || lon == null) return { x: 0, y: 0 };
 
   const currentPoint = map.project([lon, lat]);
-  const PROXIMITY_THRESHOLD = 80; // pixels
-  const MAX_OFFSET = 60; // max offset in pixels
+  const PROXIMITY_THRESHOLD = 100; // pixels - larger to detect more overlaps
 
-  const nearbyMarkers = [];
-
-  for (const marker of markersRef.current) {
-    if (!marker.post || marker.post.id === post.id) continue;
+  // Check distance in geographic coordinates (more stable across zoom levels)
+  const nearbyCount = markersRef.current.filter(marker => {
+    if (!marker.post || marker.post.id === post.id) return false;
 
     const mLat = typeof marker.post.lat === "number" ? marker.post.lat : marker.post.latitude;
     const mLon = typeof marker.post.lon === "number" ? marker.post.lon : marker.post.lng;
-    if (mLat == null || mLon == null) continue;
+    if (mLat == null || mLon == null) return false;
 
-    const mPoint = map.project([mLon, mLat]);
-    const dist = Math.sqrt(
-      Math.pow(currentPoint.x - mPoint.x, 2) +
-      Math.pow(currentPoint.y - mPoint.y, 2)
-    );
+    // Geographic distance (rough approximation)
+    const latDiff = Math.abs(lat - mLat);
+    const lonDiff = Math.abs(lon - mLon);
+    const geoDist = Math.sqrt(latDiff * latDiff + lonDiff * lonDiff);
 
-    if (dist < PROXIMITY_THRESHOLD) {
-      nearbyMarkers.push({ marker, distance: dist, point: mPoint });
-    }
-  }
+    // Small threshold for geographic clustering (~100m at equator)
+    return geoDist < 0.001;
+  }).length;
 
-  if (nearbyMarkers.length === 0) return { x: 0, y: 0 };
+  if (nearbyCount === 0) return { x: 0, y: 0 };
 
-  // Create a cascade effect: offset markers in a circular pattern
-  const index = nearbyMarkers.length;
-  const angle = (index * 45) * (Math.PI / 180); // 45 degrees apart
-  const offsetMagnitude = Math.min(20 + (index * 12), MAX_OFFSET);
+  // Use deterministic hash-based offset so it's stable across zoom/pan
+  const hash = hashPostId(post.id);
+  const angle = (hash % 8) * 45 * (Math.PI / 180); // 8 positions, 45° apart
+  const offsetMagnitude = 25 + ((hash % 3) * 15); // 25, 40, or 55 pixels
 
   return {
     x: Math.cos(angle) * offsetMagnitude,