Function install_git_catalog_skill_source 

pub fn install_git_catalog_skill_source(
    url: &str,
    skill_name: &str,
    skills_path: &Path,
    allow_scripts: bool,
    workspace_dir: &Path,
) -> Result<(PathBuf, usize)>

Install a single skill by name from a git catalog repository.

Clones url into a throwaway directory, resolves skills/<skill_name>/ (the same <repo>/skills/<name>/ layout as the default and extra registries), and installs it through the shared local-copy path (which runs the security audit). No archive handling — pure git clone.