Play through the first camera that is switched on

The game view took whatever camera came first in the scene, ignoring the
switch, so `enabled = false` on a camera did nothing and a second camera
never got its turn. `World.activeCamera()` now decides: of the cameras
switched on – the whole parent chain counted, as for any object – the
first in hierarchy order, and none on renders nothing at all. It is asked
per frame, so a graph switching cameras hands the view over immediately.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/PlaySession.ts

@@ -79,9 +79,9 @@ export class PlaySession {
     this.host.gameView.setWorld(world);
     this.host.showGame();
     this.state.setNotice(
-      world.firstOfType('camera')
+      world.activeCamera()
         ? 'Playing · edits are not saved · Esc stops'
-        : 'This scene has no camera – nothing is rendered · Esc stops',
+        : 'No camera is switched on – nothing is rendered · Esc stops',
     );
     if (world.stopRequested) this.stop();
   }