fix(sky): restore the Milky Way on teardown, tidy the anime QA script

- VisualEffects.destroy() puts skyBox.milkyWayVisibility back to 1, as it
  already restores the borrowed bloom stage, so a surviving viewer does not
  keep a faded sky.
- Rename scripts/qa-anime-space-mask.mjs to qa-anime-sky.mjs: rewrite the
  header for the current approach, drop --space-expr and --repo, import
  puppeteer as a package, reject unknown cases and count the milkyway case
  as reached only while the anime stage is on.
- Put both sky QA scripts under format:check.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/ui/visualEffects.js

@@ -115,7 +115,7 @@ export class VisualEffects {
     // Anime's four luminance bands turn the faint Milky Way into blotches, and
     // a post-process cannot tell the sky from far geometry reliably (near
     // plane clamps, keyless terrain above the ellipsoid horizon): fade the
-    // glow out with the style instead. Stars survive as banded points.
+    // glow out with the style instead. Bright stars survive as banded points.
     if (stage === this.stages.anime) {
       const sky = this.viewer.scene?.skyBox;
       if (sky && 'milkyWayVisibility' in sky)
@@ -228,7 +228,7 @@ export class VisualEffects {
     this.transitions.clear();
   }
 
-  /** Remove owned stages and restore the borrowed bloom stage after callers release it. */
+  /** Remove owned stages and restore the borrowed bloom stage and sky after callers release them. */
   destroy() {
     if (this.destroyed) return;
     this.stop();
@@ -240,5 +240,11 @@ export class VisualEffects {
       Object.assign(this.bloomStage.uniforms, this.previousBloom.uniforms);
       this.bloomStage.enabled = this.previousBloom.enabled;
     }
+    // Anime may have faded the Milky Way out; a surviving viewer gets it back.
+    const sky = this.viewer.scene.skyBox;
+    if (sky && 'milkyWayVisibility' in sky) {
+      sky.milkyWayVisibility = 1;
+      this.requestRender('style-stage');
+    }
   }
 }

src/ui/visualEffects.test.mjs

@@ -179,6 +179,24 @@ test('the anime stage fades the Milky Way out with its own intensity', () => {
   f.effects.destroy();
 });
 
+test('destroying the effects gives a surviving viewer its Milky Way back', () => {
+  const f = fixture();
+  const sky = { milkyWayVisibility: 1 };
+  f.effects.viewer.scene.skyBox = sky;
+  f.effects.initStyles();
+  f.effects.startTransition('anime', 0, 1);
+  f.tick(250);
+  f.effects.stop();
+  const frozen = sky.milkyWayVisibility;
+  assert.ok(
+    frozen > 0 && frozen < 1,
+    'stop keeps the stages, and the fade, as they are',
+  );
+  f.effects.destroy();
+  assert.equal(sky.milkyWayVisibility, 1);
+  assert.equal(f.requests.at(-1), 'style-stage');
+});
+
 test('bloom retains its dead zone, normalized intensity and independent toggle', () => {
   const f = fixture();
   f.effects.initPostProcess();