-- Store the source channel's title per video so the list can offer a real
-- channel filter (multi-select of the user's channels) instead of the dead
-- free-text field that only ever matched the provider string. Nullable: existing
-- rows backfill on the next discovery pass (UpsertVideo writes it); pasted videos
-- get it immediately from videos.list. No FK to a channels table at Stage 0 — the
-- title is a denormalised display/filter value, consistent with the existing
-- subscription_id-stays-NULL stance (data-model.md).
ALTER TABLE videos ADD COLUMN channel_title TEXT;