Use CartoDB Positron light theme for event map, matches neo-brutalist design

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

assets/modules/event-map.js

@@ -34,9 +34,10 @@ function geocodeAndRender(address, mapEl) {
             /* global L */
             const map = L.map(mapEl).setView([lat, lon], 16)
 
-            L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
-                attribution: '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a>',
+            L.tileLayer('https://{s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}{r}.png', {
+                attribution: '&copy; <a href="https://www.openstreetmap.org/copyright">OSM</a> &copy; <a href="https://carto.com/">CARTO</a>',
                 maxZoom: 19,
+                subdomains: 'abcd',
             }).addTo(map)
 
             L.marker([lat, lon]).addTo(map).bindPopup('<b>' + address + '</b>').openPopup()