Function export_backup 

pub async fn export_backup(
    ks: &Keyspaces<'_>,
    seed_store: &dyn SeedStore,
    config: &AppConfig,
    auth: &AuthClaims,
    password: &str,
    include_audit: bool,
) -> Result<BackupEnvelope, AppError>

Assemble and encrypt a backup of the entire VTA state.