Auto-resolve, per-campaign opt-in

**Per-campaign opt-in**, and never onto a date the GM hasn't marked available.

- [ ] `campaigns.auto_resolve_polls` (default off), editable in the console.
- [ ] When on: the click that makes a date satisfy the win rule canonises the poll immediately *only if* the GM has marked that date available. Otherwise the poll waits for the organiser.
- [ ] Auto-resolution posts the same notices canonising by hand would; it is not a silent path.

Start by locating how campaign settings are stored and edited in the console, then find the poll click path that evaluates the win rule and the existing manual canonisation notices. Implement the per-campaign default-off setting and availability check, and verify that eligible polls canonise with the usual notices while unavailable dates remain pending.

索引モデルが issue の本文から書いたものです。