Function normalize_str 

pub fn normalize_str(text: &str, repo_root: &Path, fs: &dyn Fs) -> Normalized

Normalize the full text of an OSS-RELEASE.md (frontmatter + body).

Split from normalize so tests can exercise the pipeline on a string without a real file. repo_root and fs are still needed for the filesystem-dependent floors (the fragment-dir path floor and its advisory existence check).