Function render_text 

pub fn render_text(
    diff: &BibDiff,
    header_a: &str,
    header_b: &str,
    use_color: bool,
) -> String

Render a BibDiff as a human-readable text report. header_a / header_b are free-form labels (e.g. file paths or “question abc123”) that go in the “=== bib diff: vs ===” line.