Runner step hover now shades the matching window on the metrics charts

Hovering a CI step on the runner Overview page now correctly shades that step’s time window across the CPU, Memory, and Network charts. The correlation highlight was broken in production because the charts were looked up via ECharts’ instance registry from a different copy of the library than the one Noora used, so the shading band was never applied. Noora now exposes its chart instance on the chart element, letting the runner metrics view apply the hover highlight reliably regardless of ECharts copy split.