Advertise `elicitation.form` in the ACP handshake and handle
`elicitation/create` requests end-to-end through the daemon.
Adds `Elicitation` transcript row kind, `pending_elicitation` to
ReducedState, the elicitation pump, persistence, and a new
`POST /api/sessions/:id/structured/elicitations/:nonce` endpoint.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>