refactor(map): extract MAP_STYLE into a shared map-style.js module

Single source of truth for the MapLibre style URL, shared between
maplibre-utils.js (multi-marker/GPX maps) and the new location-map.js
preview module — no behavior change.

themes/intotheeast/js/maplibre-utils.js

@@ -1,8 +1,9 @@
 /* Shared MapLibre GL utilities — loaded by map.html.twig, dailies.html.twig, home.html.twig */
+import { MAP_STYLE } from './src/map-style.js';
+
 (function (global) {
   var ACCENT      = '#2A8C73';
   var ACCENT_DIM  = '#155244';
-  var MAP_STYLE   = 'https://basemaps.cartocdn.com/gl/dark-matter-gl-style/style.json';
 
   /* Build a GeoJSON LineString feature */
   function lineFeature(coords) {