thread_view: Fix issues with images (#36509)

- Clean up failed load tasks for mentions that require async processing
- When dragging and dropping files, hold onto added worktrees until any
async processing has completed; this fixes a bug when dragging items
from outside the project

Release Notes:

- N/A
df9c2aefb1Cole Miller committed on 8/19/2025, 7:14:43 PM· committed by GitHubparenta91acb5
3 files changedLine totals unavailable