- Add Last upload, total Length and a Normal/Shorts/Live breakdown, computed on read in the
existing grouped query (~35ms over the full catalog — measured, so no denormalization).
- Subscribers shown compact (919K), since the YouTube API already rounds them.
- Tag cell now shows only the tags actually attached to a channel; a '+' opens a per-channel
picker to attach/detach, instead of listing every user tag on every row.