Add a notification trigger that fires when a build passes for the first time after a failure. Currently users can filter to failed-only notifications, but there's no recovery signal — leaving engineers to manually check CircleCI to know when a pipeline is healthy again.

Customer evidence:

A beta native Slack integration user specifically requested this as a complement to failed-only filtering — they want the failure-to-recovery loop closed without switching back to "all notifications" mode.

Expected outcome:

Allow users to opt-in to be notified when a pipeline recovers, reducing manual monitoring toil and completing the failure response workflow entirely within Slack.