Mark lost posting when teammate flags a message

Posting status rows go stale when flagged messages aren't recorded, causing duplicate outreach. You get an updated status and channel notice so owners stop outreach same day.

Overview

When teammates flag a posting, the tracking sheet should reflect that change immediately so sourcers stop chasing dead opportunities. This flow updates the record and pings the channel, giving program coordinators a single source of truth and stopping wasted outreach within minutes.