Plain-text diff for AI agents

[BasixKOR]

Feature Request

Allow using .diff extension to show textual diff to be consumed by AI agents.

Why it is needed

Upgrading RN is repeative job with somewhat clear on what to do (with the help of this tool), and it is kind of task that AI agents typically are great for.

Possible implementation

GitHub already exposes getting diffs so I think that would be a great starting point.

Code sample

[mikaoelitiana]

This may be similar to #410