Admin Usage Customer Activity

How one customer is actually using the API — the drill-down behind the Top Customers by Volume call count, so "246 calls" is diagnosable without a database console: which endpoints, how often, and a recent sample of both successful and failed requests.

Scoped to a single customer_id and only runs when an admin clicks the Calls count, mirroring admin_usage_customer_errors' lazy-load rationale.