Polish diff for the `edit_file` tool (#29911)

I added some padding to the editor, and removed the border around each
hunk as it would overlap in weird ways with the card container.

## Before

<img width="1148" alt="image"
src="https://github.com/user-attachments/assets/2018feaa-c847-4609-bc82-522660714b9a"
/>

## After

One Light:

<img width="1148" alt="image"
src="https://github.com/user-attachments/assets/4da1a4b6-0af2-4479-afcc-02da50178fd6"
/>

One Dark:

<img width="1148" alt="image"
src="https://github.com/user-attachments/assets/0168631d-7b76-4582-8174-c6e9c1297dc8"
/>


Release Notes:

- Improved displaying of diffs when the agent edits files.
1adb4ecc95Antonio Scandurra committed on 5/5/2025, 11:17:15 AM· committed by GitHubparent0048e67
4 files changedLine totals unavailable