The channel card's 'N videos' was actually the count of WISHED videos (0 until you
wish some) — so every channel read '0 videos'. It now shows the REMEMBERED catalog
size (from youtube_channel_videos, which fills in as a channel is enriched/opened),
falling back to 'Channel' when nothing's cached yet. Wished count is kept as a
separate wished_count field. Playlists likewise show their video count (cached when
the playlist is followed-with-videos or opened) instead of a static 'Playlist'.
list_watchlist_channels/playlists return the remembered count; the playlist detail +
follow endpoints cache the list so the count is known. 138 tests green.
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