Description:
The Pipeline Metrics page currently does not display a loading spinner or error banner for Average Duration Card, even though it relies on the same APIs as the Pipeline Overview page. To ensure consistency and prevent user confusion during API delays or failures, the Metrics page should implement the same loading and error-handling patterns already used in the Overview page.

Acceptance Criteria:

• A loading spinner is shown for Average Duration Card when data is being fetched.

• An error banner is displayed when API requests fail.

• Behaviors match the existing implementation on the Pipeline Overview page.

• No stale or partially loaded data is shown.

Why:
Improves UX and maintains consistent behavior across pages using the same backend APIs.