feat: tmux-agents v1.21.0 tracks turns instead of requests
I shipped v1.21.0 of tmux-agents, which replaces the request ledger with turn state. A running turn shows as working and an ended turn shows as idle or done, while parents show live "waiting on" text from their nearest working descendants. Replies no longer need a request ID, and a one-slot stop notice remembers the latest requester. tmux-spawn also passes agent CLI arguments after --, saves them with the sub agent and brings them back on resume.



