agent_ui: Add branch diff menu item to context menu (#51487)
Danilo Leal
created
This PR adds the recently introduced "branch diff" mention option to the
"Add Context" menu in the message editor:
<img width="450" height="582" alt="Screenshot 2026-03-13 at 9 58@2x"
src="https://github.com/user-attachments/assets/1f5102e7-9018-4a5b-992d-43befa55dcbe"
/>
Release Notes:
- N/A