This PR simplifies how we display thread timestamps in the agent panel's
history view. For threads that are older-than-yesterday, we just show
how many days ago that thread was had in. Hovering over the thread item
shows you both the title and the full date, if needed (time and date).

<img width="450" height="786" alt="Screenshot 2025-12-18 at 5  24@2x"
src="https://github.com/user-attachments/assets/11416e9b-f1b0-4307-9db0-988a95a316a1"
/>


Release Notes:

- N/A