Pick any number of channels; they OR together and every other filter applies
across the lot — "the last week's unwatched from these three".
`channelId`/`channelName` are replaced outright by `channelIds: string[]`, no
legacy reader (standing rule: no back-compat unless asked — a saved view written
against the old field simply loses its channel filter). The wire and the share
URL move with it: repeated `channel_ids` params, `?channel=a,b`. Backend ORs via
`Video.channel_id.in_()`; the count endpoint shares the same params object.
Two things the migration exposed:
- SavedViewsWidget fed DB blobs straight into serializers that now index an
array — the FeedFilters type says nothing about what an older build wrote, so
the blob is coerced where it enters. It white-screened the app before this.
- Chips carried channelName to label themselves. Without it they resolve names
from the channel cache, so they now fall back to the id, not a shared
"This channel" that would render N identical chips while the cache loads.