Function get_git_diff_from_review_baseline 

pub fn get_git_diff_from_review_baseline() -> Result<String>

Get the diff from the review baseline (or start commit if baseline not set).

This function provides a per-review-cycle diff, falling back to the original start_commit if no review baseline has been set.

Returns

Returns a formatted diff string, or an error if:

• The repository cannot be opened
• The baseline commit cannot be found
• The diff cannot be generated