The `backup_parent_seed` API endpoint was vulnerable to arbitrary file write via path traversal.
The `path` parameter was used directly to create a `Path` object, which was then passed to `_pm.handle_backup_reveal_parent_seed`.
This allowed an attacker to specify an arbitrary path (e.g., `../../evil_file`), which would be used by `encrypt_and_save_file` to write the encrypted seed to that location.
This commit fixes the vulnerability by validating that the `path` parameter is a valid filename (i.e., does not contain path separators or parent directory references) before processing it. This ensures that the backup file is always created within the intended fingerprint directory.
Co-authored-by: PR0M3TH3AN <[email protected]>