Send implemented feedback email to assigned coach immediately

Coaches aren't notified when feedback is marked Implemented, so they miss update context. It sends a contextual email to the assigned coach so they can acknowledge updates the same day.

Overview

When feedback is marked implemented, coaches often miss the change and can't act on updates; this flow closes the loop by emailing the assigned coach with context. That clarity reduces follow-up friction and lets managers confirm or act on updates the same day.