- Update useFlashOnIncrease default duration from 700ms to 1400ms
- Update CSS count-flash-bg animation duration to 1400ms
- Update test assertions to match new 1400ms duration
- Set task status to 'failed' on execution failure in engine executor
- Add failed indicator styling on TaskCard component
- Add POST /tasks/:id/retry API endpoint and client function
- Add retry button in TaskDetailModal for failed tasks
- Add tests for failed indicator, retry endpoint, and modal behavior