update_channel: payload:dict → ChannelUpdateIn (priority/hidden/deep_requested,
all optional for PATCH semantics). Kills the `int(payload["priority"])` 500 the
prod report hit — a non-numeric/garbage value now returns 422, not 500.
attach_tag: payload:dict → AttachTagIn(tag_id:int) — a non-int tag_id was a 500
in `db.get(Tag, ...)`; the personal-tag ownership check reuses owned_or_404.