The doctor command runs entirely inside Claude Code and walks through:
binary install via npm, daemon autostart, mailbox-name prompt with write
to per-project `.claude/settings.json` env, and a self → self smoke test.
Also adds `/claude-mailbox:mailbox-status` as a read-only health check.
Reduces the colleague onboarding to: add marketplace, install plugin,
run the doctor — no terminal context-switch required.
