Cover raised imagery shells on the headless Cesium engine

Exercise the real shell primitives and materials over the headless engine.
Cover raised rectangle geometry, alpha and depth policy, camera lift, shell
ordering, upload readiness, hidden frames, detail replacement and moved
windows, render idling and resource cleanup. Drive the public imagery API
through detail bounds and staged source settlement as well. Supply only the
geometry and texture completion signals that require a renderer.

Preserve Cesium's reference behavior without changing runtime code. Navara
and the fake engine are unchanged. Include the new test in the format scope.

All eleven coupling counts remain unchanged; none fell or grew. Renderer
lines remain 0 and 189, external Cesium import files 3, viewer lines 891,
Navara kind checks 1, engine-sniff calls 0, extension reads 3, ground passes
1, SDK loads 3, screen-handler files 4 and engine-name lines 32.

scripts/format-scope.json

@@ -1643,6 +1643,7 @@
   "scripts/qa-weather-compare.mjs",
   "src/globe/cesium/imagery.js",
   "src/globe/cesium/imagery.test.mjs",
+  "src/globe/cesium/imageryShell.test.mjs",
   "src/globe/imagery.js",
   "src/globe/imagery.test.mjs",
   "src/globe/navara/imagery/index.js",