NotifyROIDestroyed now walks the parent chain to also invalidate child
ROIs of the destroyed performer (head, limbs, etc.) that were placed
into the roiMap by BuildROIMap. The ancestor walk happens once; all
other fields are cleaned with simple pointer equality.
When a remote player's ROI is destroyed (disconnect, timeout, or respawn),
notify all active ScenePlayer instances to null out dangling references
before the ROI is freed. The animation engine already handles null ROI map
entries gracefully, so playback continues for remaining participants.
