refactor: extract application construction and lifecycle

src/app/viewer.js

@@ -0,0 +1,35 @@
+import * as Cesium from 'cesium';
+
+/** Create the standard globe viewer in caller-owned, visible containers. */
+export function createApplicationViewer({ container, creditContainer }) {
+  if (!container || !creditContainer) throw new TypeError('Viewer and credit containers are required');
+  const viewer = new Cesium.Viewer(container, {
+    timeline: false,
+    animation: false,
+    baseLayerPicker: false,
+    geocoder: false,
+    homeButton: false,
+    sceneModePicker: false,
+    navigationHelpButton: false,
+    fullscreenButton: false,
+    vrButton: false,
+    selectionIndicator: false,
+    infoBox: false,
+    baseLayer: false,
+    creditContainer,
+    msaaSamples: 4,
+    contextOptions: { webgl: { preserveDrawingBuffer: true } },
+  });
+  try {
+  viewer.targetFrameRate = 60;
+  viewer.scene.globe.show = false;
+  viewer.scene.skyAtmosphere.show = true;
+  viewer.scene.skyAtmosphere.atmosphereLightIntensity = 18;
+  viewer.scene.skyAtmosphere.saturationShift = -0.12;
+  viewer.scene.skyAtmosphere.brightnessShift = -0.08;
+  return viewer;
+  } catch (error) {
+    viewer.destroy();
+    throw error;
+  }
+}