🔧 Cluster map markers for dense areas

[fusion94]

Summary

MapView renders one MarkerF per user with no clustering (src/components/LocationMap.jsx). At 100+ members in a single metro the map becomes unreadable. Use MarkerClusterer from @react-google-maps/api (already a dependency) to group nearby pins.

Proposed Approach

1. Wrap the otherUsers markers in <MarkerClusterer>.
2. Keep the current user's own marker outside the cluster so it always stays visible.
3. Style the cluster bubbles to use the brand gold (theme.palette.primary.main).
4. Test with the existing dev data plus a synthetic 100-user dataset.

Acceptance Criteria

• Multiple markers in the same area cluster into a single bubble showing the count.
• Zooming in expands the cluster.
• The current user's own marker is never clustered.
• Cluster icon color matches the brand accent.
• Works in both light and dark themes.