Admin Customer Usage

Usage-over-time + current billing period credit spend for one customer.

Powers the "View Usage & Performance" panel launched from the Customer detail offcanvas. Two distinct pictures, both scoped to this customer:

• daily_trend: product calls (REST + MCP tools/call), handshake volume, errors/latency/credits from api_usage_log over a selectable rolling window — "performance over time". Handshake initialize/ tools/list/ping is kept as a separate series so reconnect storms don't look like product usage.
• billing_period / billing_period_daily: the exact credits picture the customer sees on their own Dashboard (get_current_usage — same credit_usage-backed source of truth used by the Customer panel's credits bar), plus a day-by-day breakdown within that billing period.