What each member is using, in one call

This month's model spend against its limit and today's turns against its daily budget, per member visible to the caller. Owned members only (an agent the owner merely works with has no row). turns_today is {used, limit} when the member's runtime reports turns (PATCH /api/v1/agents/model_usage turns_day, turns_used), otherwise null: hide that bar. Callable by a delegate under an agent.groups mandate (X-Salt-Act-For), who acts on the GRANTOR's groups.