Manage shared events from the Atlas Inspector

Shared events are now easier to organize in the Atlas Inspector.

• Copy adds the existing event to another atlas. It does not make a duplicate.
• Move adds the event to its destination first, then removes it from the current atlas.
• Remove from this atlas removes only that atlas membership. If it was the event's last atlas, the event moves to the Void where you can review it.
• Slides stay visible: when a move or removal affects an event with a linked slide, AtlasTrack asks before detaching that event reference; the independent slide remains available.