feat: add reading_status_push auto-refresh schedule per library

- Migration 0059: reading_status_push_mode / last / next columns on libraries
- API: update_reading_status_provider accepts push_mode and calculates next_push_at
- job_poller: handles reading_status_push pending jobs
- Indexer scheduler: check_and_schedule_reading_status_push every minute
- Backoffice: schedule select in library settings modal

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/backoffice/app/(app)/libraries/page.tsx

@@ -147,6 +147,7 @@ export default async function LibrariesPage() {
                       fallbackMetadataProvider={lib.fallback_metadata_provider}
                       metadataRefreshMode={lib.metadata_refresh_mode}
                       readingStatusProvider={lib.reading_status_provider}
+                      readingStatusPushMode={lib.reading_status_push_mode}
                     />
                     <form>
                       <input type="hidden" name="id" value={lib.id} />