Desktop PR monitor: add "merge when green" without archiving the session

The Code tab's PR monitor offers Auto-fix, which wakes the session on CI failures, conflicts and review comments, and Auto-archive on merge. The session is also told never to poll CI itself.

A common workflow sits between the two. I tell Claude, per PR, "merge and deploy when CI is green". Claude then merges, runs the deploy, verifies it, and the session continues with the next task. Before the monitor existed, Claude did this with gh pr checks --watch in the background.

Today that isn't possible in the desktop app:

• Auto-fix sends no event when checks turn green.
• The Auto-merge toggle is GitHub auto-merge. It is a repo-level setting rather than a per-PR decision, and it can't run the post-merge steps (deploy, verification).
• Self-polling is forbidden.

Request: a <ci-monitor-event> when all required checks pass, for example an "On green: wake session" switch. The agent could then act on a conditional instruction the user gave for that specific PR. Alternatively, allow agent-side polling when the user explicitly asks for it.