Function has_roxygen_tag 

pub(crate) fn has_roxygen_tag(tags: &[String], tag: &str) -> bool

Return true if the tag list contains a specific roxygen tag.

Supports both single-word tags (e.g., "export", "noRd") and multi-word tags (e.g., "keywords internal"). For single-word tags, matches the first word after @. For multi-word tags, matches the full content after @ (trimmed).