- Add --as user support to +messages-send and +messages-reply
- Add UserScopes (im:message.send_as_user) / BotScopes (im:message:send_as_bot)
- Add DoAPIAsBot to RuntimeContext so file/image uploads always use bot
identity even when the surrounding command runs as user
- Update skill docs and reference files to reflect user/bot support
- Default identity remains bot (first element of AuthTypes)