fix(map): atomic boundary transition when switching places

Remove the clear-then-set pattern when clicking a new labeled feature.
Previously, clicking Kimberly after Twin Falls would:
1. Clear Twin Falls boundary
2. Set new place
3. Wait for API to return
4. Set Kimberly boundary

This caused the old boundary to disappear before the new one was ready,
requiring two clicks.

Now when clicking a new labeled feature:
1. Set new place immediately
2. When API returns, updateBoundary(newData) replaces old data in-place

The GeoJSON source only holds one dataset - setting new data naturally
replaces old data. Explicit clear only needed when deselecting or
clicking empty map.

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

src/components/MapView.jsx

@@ -1280,8 +1280,7 @@ const MapView = forwardRef(function MapView(_, ref) {
             highlightedFeatureRef.current = null
           }
           setSelectedHighlight(map, null)
-          // Clear old boundary before setting new place
-          if (updateBoundaryRef.current) updateBoundaryRef.current(null)
+          // Note: do not clear boundary here - new data replaces old when API returns
 
           if (labelFeature) {
           // Clicked a labeled feature — snap to geometry and highlight