Salvaged from #45765 by @navahc09 — kept the PR's callout structure
and placement, rewrote the content to match current behavior:
Slack blocks native slash commands in threads and never delivers them,
so Hermes recognises a leading '!' as an alternate command prefix.
Post-C3 command fixes the bang form also works behind a mention
(@Hermes !cmd) and with leading whitespace; unknown '!' tokens pass
through to the agent unchanged. Cross-linked the detailed
slack.md section.
2b226be8e3