dashboard-add-retry-backlog-panels

Instruction

Could you update the saved "Service Overview" dashboard (`service-overview`) so on-call can see retry pile-up directly during incidents? Add a timeseries panel titled exactly "Retry Backlog" that compares payment-service against order-service backlog depth over time, a stat panel titled exactly "Peak Payment Retry Backlog" that surfaces the payment-service peak over the dashboard time range, and a second stat panel titled exactly "Order Spillover Share" that shows roughly how large the order-service peak backlog was relative to the payment-service peak. Keep the existing panels in place.