Draft: feat: enhance agent test run UI experience
Relates to issue #557569 (closed)
This MR was created by Duo in Session 1112166
Changes
- Implement frontend improvements for agent test run UI based on UX design from work item #563127 (closed)
- Replace redirect with success alert containing session link for better user context preservation
- Enhance error handling to show proper error alerts instead of success toasts
- Improve UI consistency with existing GitLab patterns and user experience flows