pub fn ensure_scc_ignored(root: &Path)Expand description
Ensure .scc/ is gitignored so the index cache never pollutes the
repo’s own git status or gets committed — except .scc/intent.yaml,
which is committable repository intent, not cache. A bare .scc/
pattern would make git (and our own gitignore-respecting walker) prune
the whole directory including intent, silently dropping declared
components and flows. Idempotent, never touches other lines.