Adds a configurable schedule (manual/hourly/daily/weekly) for the
download detection job in the library settings modal. The indexer
scheduler triggers the job automatically, and the API job poller
processes it — consistent with the reading_status_push pattern.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
The scheduler (indexer) created metadata_refresh/metadata_batch jobs in DB,
but the indexer excluded them (API_ONLY_JOB_TYPES) and the API only processed
jobs created via its REST endpoints. Scheduler-created jobs stayed pending forever.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>