feat(scenes): render the Scene panel's controls from the store

SceneControls no longer takes element handles or writes the Scene panel's
button states, PLAY label, status line, progress bar or runtime chip: it
presents them to the gev-scenes store, and the panel's buttons, scene
select and IMPORT chooser call its actions there. The chooser opens only
while an owner presents the panel and is cleared once its import settles.
On destroy the panel keeps its last status and buttons, without shots or
the runtime chip, as before.

scripts/qa-scene-controls.mjs

@@ -446,8 +446,7 @@ try {
     const retainedLabel = document.querySelector('.scene-shot-label');
     const stopping = director.destroy();
     const notificationsAtStop = window.__qaSceneState.length;
-    const stoppedSynchronously =
-      controls.destroyed && controls.removers.length === 0;
+    const stoppedSynchronously = controls.destroyed;
     retainedLabel?.click();
     document.getElementById('scene-new-btn').click();
     controls.run('capture');