Add subteam-tagged messages to support daily update digest

Subteam-tagged messages get lost in busy channels, leaving customer issues untriaged and absent from daily reports. Collect them in a daily digest so support ops prepare briefs before the stand.

Overview

When subteam mentions are buried in busy channels, support ops waste time hunting for context. This captures tagged messages into a central daily digest so support leads can triage with full context and prepare briefings before the daily stand.