cleanup-branches

Prune local branches whose work is already merged into the base. TRIGGER when the user says "clean up branches", "delete merged branches", "prune local branches", "remove old branches", "I have too many branches", "what branches can I delete", "/nyann:cleanup-branches". Do NOT trigger on "delete THIS branch" (that's a one-off `git branch -D`, not a cleanup pass) or "remove a branch from the remote" (this skill is local-only; remote pruning is `git push --delete origin <branch>` and the user should do that themselves). Do NOT trigger on "merge this branch" (that's the merge step before cleanup).

适合你，如果本地积累了大量已合并的旧分支需要清理。