Address the two remaining review findings on the tag work:
- extract useChannelTagActions — the optimistic attach/detach + create-and-attach flow that
the channel manager and the channel detail page had copy-pasted; the cache-shape-specific
optimistic update is injected (manager maps a ManagedChannel[]; detail patches one
ChannelDetail), so the two stay in sync;
- add a DB-lane test asserting GET /api/channels/{id} returns exactly this user's personal
tag links — not another user's, not the auto/system (user_id NULL) links.
peter
f091247624