refactor(maps): separate source factories and scene coordination

src/maps/imagery.js

@@ -0,0 +1,29 @@
+import * as Cesium from 'cesium';
+
+// Attribution and service rights are documented in DATA_SOURCES.md.
+export const ESRI_ATTRIBUTION_HTML =
+  '<a href="https://www.esri.com" target="_blank" rel="noopener">Powered by Esri</a>';
+
+export function createOsmImagery() {
+  return new Cesium.OpenStreetMapImageryProvider({
+    url: 'https://tile.openstreetmap.org/',
+    credit: '© OpenStreetMap contributors',
+  });
+}
+
+export function createEsriImagery() {
+  return Cesium.ArcGisMapServerImageryProvider.fromUrl(
+    'https://services.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer',
+    {
+      credit:
+        'Powered by Esri — Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community',
+      enablePickFeatures: false,
+    },
+  );
+}
+
+export function createIonImagery(style, accessToken) {
+  accessToken = String(accessToken || '').trim();
+  if (!accessToken) throw new Error('Ion imagery requires an explicit token');
+  return Cesium.IonImageryProvider.fromAssetId(style, { accessToken });
+}