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/package-boundaries.json

@@ -1737,6 +1737,20 @@
       "src/app/layers/traffic.js",
       "src/app/operations.js",
       "src/app/scene.js",
+      "src/app/globeEngine.js",
+      "src/globe/contract.js",
+      "src/globe/cesium/createCesiumEngine.js",
+      "src/globe/cesium/camera.js",
+      "src/globe/cesium/convert.js",
+      "src/globe/cesium/credits.js",
+      "src/globe/cesium/events.js",
+      "src/globe/cesium/frames.js",
+      "src/globe/cesium/input.js",
+      "src/globe/cesium/maps.js",
+      "src/globe/cesium/picker.js",
+      "src/globe/cesium/projector.js",
+      "src/globe/cesium/render.js",
+      "src/globe/cesium/surface.js",
       "src/sources/sourceSlot.js",
       "src/app/sources.js",
       "src/app/startupChrome.js",