Delete Poll

Creator deletes a scheduling poll outright, in ANY state.

Until this existed the only way out of a poll was reopen with {"cancel": true}, and the UI only offered that inside the FINALIZED block. So an open poll - the state a poll spends nearly all its life in, and the state of every poll created by mistake - could not be removed at all. It sat in the channel feed forever (Nancy hit this demoing polls to Mariana, 2026-09-04).

Removes, in one transaction: the scheduled room and its RSVPs (if the poll had been finalized), the poll_invite card(s) in the channel feed, every response (via the relationship cascade), and the poll row itself.