See who else is editing a shared project

When someone opens a project you’ve shared with them, you now see them: an avatar for each collaborator in the toolbar, plus their live cursor and current selection on the canvas as they move around and pick layers. It’s presence only for now — you still edit separately without conflicts, but you can finally tell who’s in the file with you and roughly what they’re looking at.

This lays the groundwork for actual co-editing, where changes from multiple people land in the same document live. Presence stays off for solo editing, so nothing changes if you’re not working from a shared link.