_safe_skills_path() is the sibling of iter_skills_files(): when a symlink in
skills/ forces a sanitized copy for mount-based backends (Docker/Singularity),
it rglob-copied the whole tree — .hub, .curator_backups, node_modules and all.
Prune EXCLUDED_SKILL_DIRS before descending, same rule as the sync generator,
so the mounted copy never carries (or walks) the bookkeeping trees either.