Feature request: add /me support to chats

I would like to request keybase chat include a /me function like Slack/IRC where it will display the username first followed by the text

For example: "/me says hi" would show "fleish says hi"

The issue names no files, tests, or entry points. Start by locating Keybase chat message handling and existing command behavior, then confirm how `/me says hi` should render with the username first. Done means `/me` messages display the sender followed by the supplied text, with coverage for the example.

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