Show YouTube-sourced playlists with a YouTube icon; they're read-only for now (no
rename/delete/reorder/remove, excluded from the add-to-playlist popover) with a
'synced from YouTube' note — editing comes with the write-back phase. Add a 'Sync from
YouTube' button in the Playlists rail (api.syncYoutubePlaylists) with a result toast.
Trilingual strings.