Add distance scale bar and user-placed location pins to the offline maps viewer.
- Scale bar (bottom-left) shows distance reference that updates with zoom level
- Click anywhere on map to place a named pin with color selection (6 colors)
- Collapsible "Saved Locations" panel lists all pins with fly-to navigation
- Pins persist in localStorage across page loads
- Full dark mode support for popups and panel via CSS overrides
New files: useMapMarkers hook, MarkerPin component, MarkerPanel component
No backend changes, no new dependencies.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
