fix(sky): preserve dark model lighting and address review

Merge origin/main and retain both format-scope additions.
Give StarrySky a separate black environment cube map and release it on destroy.
Guard anime updates when StarrySky is absent, require a visible Normal sky
before anime QA, and compare a lit airplane against black and white controls.
Document the sky background contract and its verification.

Co-Authored-By: GPT-6 (Codex) <[email protected]>

src/app/layers/streetLevel.js

@@ -32,21 +32,11 @@ function defaultProviders(sources) {
  * including when the list is empty.
  */
 export function createApplicationStreetLevel({
-  surface,
   sources = {},
   providers = defaultProviders(sources),
 }) {
   return createStreetLevelLayer({
     providers,
-    services: {
-      sprites,
-      picking,
-      input,
-      scenePick,
-      render,
-      ground: surface?.groundFloor ?? null,
-      meshFloor: surface?.meshFloor ?? null,
-      terrain: surface?.terrain ?? null,
-    },
+    services: { sprites, picking, input, scenePick, render },
   });
 }