enrich_pending only touches enriched_at IS NULL, so a video first seen
while live was stamped live + duration-null and never revisited — staying
'live' with no duration forever after the broadcast ended. Add refresh_live
(run after each enrich pass) that re-fetches anything still live/upcoming,
plus just-ended was_live videos that haven't got their duration yet, until
they settle. Cheap: videos.list is 1 unit per 50 ids.