Changes

feat(scripts/ops): add cherry-pick branch cleanup script (#3473)

Safely removes merged cherry-pick branches by
checking for open PRs before deletion. Works across multiple repos
(tidb, tiflash, tiflow, tikv, pd) using the GitHub API.

Usage:
```bash
deno run --allow-net scripts/ops/clean-cherry-pick-branches.ts -token <github token>
```
 (commit: d553ef2)