Function replace_wikilinks 

pub fn replace_wikilinks(
    content: &str,
    old_slug: &str,
    new_title: &str,
) -> String

Replace all \[\[wikilinks\]\] that resolve to old_slug with new_title. Preserves aliases: [[Old|alias]] -> [[New Title|alias]]. Uses pulldown-cmark to skip links inside code blocks and inline code spans.