Delete thread button on hover

Add a delete thread button on hovering over a thread in the sidebar. Similar to the codex app.

<img width="533" height="289" alt="Image" src="https://github.com/user-attachments/assets/86a0bbfd-a26f-48ba-b6a9-c37066ffb4e4" />

<img width="413" height="176" alt="Image" src="https://github.com/user-attachments/assets/799f0cb6-b5dd-498d-a751-c995d511de8b" />