kill-session-after-min clarified: idle/prompt-parked sessions are released, not killed, at the cap

The help text for --kill-session-after-min now clarifies what actually happens at the wall-clock deadline: a session that is idle, parked at a permission prompt, or still starting up is released (paused server-side and resumable) rather than killed. Only a session with a turn still running, or one where the server keeps declining the release, gets SIGTERMed at the hard cap.