The catalog only stores the recent-backfill/RSS subset of a channel's uploads (video_count is
YouTube's raw total), so a subscribed channel looked like it was "missing" videos. Now the channel
page header shows "{stored} / {total} videos" when there's a gap, and a "Full history" action queues
the deep backfill (the same deep_requested trigger the channel manager uses) — showing a loading
state until done. Backend: channel_detail now returns deep_requested/backfill_done.