List webhook event catalog

Self-describing catalog of every webhook event type: its description, data payload shape, and whether it is active (has a firing producer) or dormant (subscribable but not yet delivered). The catalog is identical for every authenticated key and exposes no owner-scoped data. Pro-only event types (whale_trades_inserted, wallet_grade_changed, insider_radar_flag_raised, smart_money_flow_detected) appear in the catalog but only deliver to API keys on an active Pro subscription.