feat(smart): record and display SMART self-test results #491

Summary

Short and long SMART self-test results should be recorded by the collector and displayed in the device detail UI.

Why

SMART self-tests provide valuable health indicators that complement attribute monitoring. Currently the collector does not capture self-test history, and there is no UI to view results or trigger tests.

Acceptance Criteria

• Collector captures self-test log from smartctl output
• Self-test history stored and retrievable via API
• UI displays self-test history in device detail view
• (Stretch) UI allows triggering a short or long self-test on demand