0012_crawler.sql's partial index on `state IN ('pending','failed')`
indexes a state that no code path ever writes — ack_failed in
crawler/jobs.rs only ever moves jobs to 'dead' or 'pending'. The
'failed' branch costs a write on every state change without ever
matching a query. Drop it; the CHECK still allows 'failed' so a
future migration can re-introduce it cleanly.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
