SABnzbd: Orphan-job path traversal permits arbitrary file deletion

SABnzbd is an open source automated Usenet download tool. Prior to 5.1.0Beta3, orphan-job management in `sabnzbd/api.py` accepts the user-controlled `value` parameter without path confinement before `os.path.join()` with `download_dir`. An absolute path discards that base directory. An attacker with a valid API key can invoke `mode=status` with `name=delete_orphan` to reach `_api_delete_orphan` and `remove_all()` in `sabnzbd/filesystem.py`, which uses `shutil.rmtree()` for recursive deletion. The advisory also identifies `_api_add_orphan` and `_api_delete_all_orphan` as affected by the path-validation issue, while its concrete arbitrary-deletion trace is through `_api_delete_orphan`. The API key is stored in plaintext in `sabnzbd.ini`. The attacker can delete files or directories writable by the SABnzbd process, including configuration, queue data, and downloads, but system files outside the regular user's ownership are not affected. This issue is fixed in version 5.1.0Beta3.