Remove grey background behind custom map marker icon

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

assets/modules/event-map.js

@@ -45,6 +45,7 @@ function geocodeAndRender(address, mapEl) {
                 iconSize: [40, 40],
                 iconAnchor: [20, 40],
                 popupAnchor: [0, -40],
+                className: 'leaflet-marker-custom',
             })
 
             L.marker([lat, lon], { icon }).addTo(map).bindPopup('<b>' + address + '</b>').openPopup()