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.

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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.