Move a folder to a new parent (or to root if parent_folder_id is null).

ADMIN on the folder being moved, EDITOR on the destination — the same pair PATCH /files/{id}/move has always required (user_files.py), and this endpoint is why that asymmetry mattered.

A CONTAINMENT edge propagates the parent's level UNCHANGED (permissions/adapters/edges.py), and creating a folder makes the creator its ADMIN. Before creation required a company admin/owner, "EDITOR on the moved resource, nothing on the destination" let any member create a folder they administer, move something they merely edit into it, and come out ADMIN on it — plus ADMIN on every database beneath it, which drops those databases' row policies entirely (row_policy.py's admin_db_ids bypass) and confers grant/revoke rights. Requiring ADMIN on the moved folder means the mover already had the level the move would confer.

Returns 409 if the move would create a circular reference and 422 if the destination holds another kind (pipeline versus workflow).