- Add path-clean dependency to sanitize file paths
- Fix 7 CodeQL path injection vulnerabilities in src/commands/setup.rs:
  * Alert #13: hooks_dir.exists() with unsanitized path from git config
  * Alert #12: hooks_dir.exists() with unsanitized global hooks directory
  * Alert #11: fs::rename() with unsanitized backup path construction
  * Alert #10: fs::set_permissions() with unsanitized file path
  * Alert #9: fs::write() with unsanitized file path
  * Alert #8: fs::create_dir_all() with unsanitized prepare_commit_msg_path
  * Alert #7: fs::create_dir_all() with unsanitized local hooks directory

- Use PathClean::clean() to normalize paths and remove directory traversal sequences
- Ensure all file system operations use sanitized paths to prevent path injection attacks
- Maintain backward compatibility and pass all existing tests

Fixes: GitHub Security Advisory alerts #7-#13