fix(sync): re-enrich live videos so ended streams gain duration

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.

backend/app/sync/runner.py

@@ -21,6 +21,7 @@ from app.sync.videos import (
     enrich_pending,
     poll_rss_channel,
     reconcile_full_history,
+    refresh_live,
     run_shorts_classification,
 )
 from app.youtube.client import YouTubeClient
@@ -65,6 +66,10 @@ def run_enrich(db: Session, max_batches: int = 200, floor: int = 200) -> int:
             total += n
             if n == 0:
                 break
+        # Revisit transient live/upcoming videos (enrich_pending is one-shot) so an ended
+        # stream gains its final duration + was_live status instead of staying "live" forever.
+        if quota.remaining_today(db) > floor:
+            total += refresh_live(db, yt)
     return total