Slack skill
Use the Slack Web API. SLACK_BOT_TOKEN must be in env.
Endpoints
post→chat.postMessagereply→chat.postMessagewiththread_tsread-history→conversations.historyreact→reactions.addupload→files.upload(orfiles.uploadV2for >5MB)
Endpoints are at https://slack.com/api/<method>. Token goes in
Authorization: Bearer .... Body is application/json for most modern
methods.