Composite event-health snapshot (one round-trip for dashboards)

Fans out internally to spread / arbitrage / settlement / dispute / edge half-life / recent anomalies / recent trades and returns a single JSON blob. Slow path — call once per dashboard refresh, not per UI tick. Use the individual endpoints (`:id/spread`, `:id/arbitrage`, …) for streaming or partial data. Anomaly window is the trailing 7 days (matches the edge-half-life recompute window); recent-trades cap is 20.