Every background job now reports progress, so the dashboard can show a live
bar for any run (not only enrich/backfill/shorts/maintenance): rss_poll and
subscriptions (runner), autotag, and playlist_sync gained progress.report
calls over their loops.
RSS polling now fetches the channel feeds concurrently (16 workers) instead
of one-at-a-time — a slow/unreachable feed no longer blocks the rest, cutting
a full poll of the catalogue from minutes to seconds. Feed fetches are
network-bound and run in the pool; DB inserts stay on the session's thread
(SQLAlchemy sessions aren't thread-safe), applied as each fetch completes.
Split the DB-write half of poll_rss_channel into apply_rss_feed so the fetch
and apply phases compose cleanly.
6eb552fa04