feat(app): construct the globe engine with the viewer

The scene builds the page's Cesium engine right after the viewer
(src/app/globeEngine.js), names the startup Google tileset to it once
loaded, returns it beside the viewer and destroys it before the viewer.
The debug handle exposes it as window.__godsEyeView.engine. Nothing
consumes it yet; render holds taken before the governor is installed
apply at install.

qa-globe-contract now runs on the app's engine (self-built only when the
app has none); a throwaway engine checks creation and destroy leave the
scene untouched.

scripts/format-scope.json

@@ -736,6 +736,8 @@
   "src/globe/cesium/createCesiumEngine.test.mjs",
   "src/globe/cesium/testing/fakeViewer.mjs",
   "scripts/qa-globe-contract.mjs",
+  "src/app/globeEngine.js",
+  "src/app/globeEngine.test.mjs",
   "src/sources/reference.js",
   "src/sources/reference.test.mjs",
   "src/search/nominatim.js",