Add a generic 'custom' channel plus an --agent-cmd flag so 'dws devapp
robot connect' can forward to ANY headless AI CLI (question appended as
the trailing arg, stdout used as the reply). Onboards tools that aren't
built-in (e.g. LobsterAI) or self-built agents with no code changes:
--agent-cmd forces channel=custom unless --channel is set explicitly,
and auto-detection falls back to custom when DWS_AGENT_CMD is present.
Also (issue #39): print a one-time hint at connect start when neither a
work dir nor a knowledge source is set, pointing at --agent-workdir /
--knowledge-* / --agent-model so the bot can match terminal answer
quality. Quickstart gains matching FAQ entries plus a note that step 3
(robot connect) produces no approval ticket (issue #19).
修雨
b4c9db8807