Summary

Fixed the thread deletion issue by:

1. Click handler conflict between the trash icon and the main ListItem
2. Added `cx.stop_propagation()` to prevent the click event from
bubbling up to the parent ListItem's click handler
3. Followed the established `cx.stop_propagation()` pattern used
throughout the codebase

Now when you click the trash icon to delete a thread:
- ✅ The thread deletion happens immediately on the first click
- ✅ No race condition between deletion and activation
- ✅ No double-clicking required

The fix is minimal, follows established patterns, and addresses the
exact root cause of the issue.

- Stop event propagation in thread removal handler

Release Notes:

- agent: Improved delete thread action in the history view by preventing
it from also triggering the thread activation.