Function render_changelog_body 

pub fn render_changelog_body(
    sections: &[(ChangelogHeading, Vec<String>)],
) -> String

Render sections (from changelog_sections) as Keep-a-Changelog markdown: each section’s heading line, a blank line, then one - {subject} line per bullet, with a blank line between sections. Returns an empty string when sections is empty — the “nothing changed” fallback text is crate::ship::prepend_changelog’s responsibility, not this function’s.