Release the waiting agent on No change or tab close

[TrickRiggin]

Problem

Send is disabled when there is nothing to comment, so a review that already looks fine has no way to end except waiting out the poll timeout. Closing the tab also left the agent hanging — I kept finding leftover human-review poll processes after I was done.

There was already a faint End review control, but it was easy to miss, required a confirm even when nothing was unsent, and did not persist, so a retry poll after timeout would hang again.

Change

• No change is the primary empty-state action (no confirm). If there is unsent feedback, it stays End review with the existing confirm.
• Closing the last review tab is the same decision after a 4s grace, so a refresh can reconnect.
• {"status":"closed","reason":"no_change"|"window_closed"} is persisted until the next human-review <file>, so a retry poll does not hang.
• Skill/setup copy tells agents to stop on closed and not to leave poll running in the background.

Tests

• Ending a review still releases the poller and keeps unsent comments
• A later poll on the same target stays closed; a new session reopens it
• Closing the last tab releases the poller with window_closed
• Reconnecting inside the grace window does not end the poll