Per-person, per-model consumption for the org

Query-time aggregation of token/request consumption grouped by attributed person, provider, and model, scoped ONLY to the org's own usage_events via the immutable attribution_org_id snapshot (MNE-3213). Consumption only — never spend/cost/currency; see GET /orgs/{org_id}/costs for the dollar-cost rollup. Billing-shaped: owner, admin, and auditor only (member/viewer never receive this data). days is restricted to 7, 30, or 90 for v1. Cursor pagination is deterministic on (total_tokens DESC, user_id, provider, model); totals and attribution_rate are computed over the complete filtered result before pagination. Behind the USAGE_ATTRIBUTION_API_ENABLED flag (default false in every environment) — while disabled this returns 404 to every caller, including owners.