Fledge IoT Gateway Backup Restore OS Command Injection via Tar Member Filename

Fledge's backup-restore upload handler, upload_backup() (python/fledge/services/core/api/backup_restore.py), takes the first extracted tar member's filename (tar_file_names[0]) and builds a shell command via string formatting: `cmd = "cp {} {}".format(source, backup_path); ret_code = os.system(cmd)`. The only pre-check on the filename is a prefix/suffix match (startswith(backup_prefix), endswith(valid_extensions)), which a name such as `fledge_backup_$(id>/tmp/pwn).db` satisfies while still injecting a shell command substitution. Because os.system() invokes a shell and no quoting (shlex.quote, list-form subprocess) is applied, an admin uploading a crafted backup archive achieves arbitrary OS command execution.