Improve highlighting on diffs a la delta or github

What variant of Codex are you using?

Codex CLI

What feature would you like to see?

Diffs are easier to read when the sections of the line that are changed are highlighted, a la delta or the standard way diffs are displayed on GitHub. If that could be done when Codex CLI is displaying diffs to the use during edits, it would make noticing problems or concerns easier.

In case what I mean isn't obvious, this is the diff style in question (as shown on delta's examples page, delta itself is at https://github.com/dandavison/delta but I'm not suggesting you use delta itself.)

<img width="1778" height="2026" alt="Image" src="https://github.com/user-attachments/assets/e4658215-7f12-40bb-bef9-b23019e19866" />

Additional information

_No response_