v3.5.1: Agent Hub folder stack stays together

Fix

•	With + New Recruit open, Agent Hub's folder stack no longer splits in two. Before, a strip of empty folder showed above + New Recruit and the top Agent's folder rode up over the Cover Identity note.
•	The folders now overlap by where they stand on screen, so the stack stays in one piece whichever folder is open.

Frontend only: no backend, rules or Cloud Functions change.