Volume / outcome / latency rollup over the desk's traces.

Definitions the UI depends on:

• answers = traces whose outcome does NOT start with refused; refusals = the rest (refused_spam / refused_adversarial).
• every latency aggregate is over ANSWERS ONLY — a refusal's duration is classifier time, and pooling it would flatter the p90.
• daily buckets are date(created_at) in UTC (created_at is written with datetime.utcnow), newest first, days with no rows omitted.