/**
 * Return the current day of month using the system timeZone.
 *
 * - Uses Temporal.Now.zonedDateTimeISO to get current day in system timezone.
 * - Returns zero-padded string (e.g., "29").
 * - Returns "" when system timezone is unavailable.
 *
 * @returns current day string (zero-padded) or "" on invalid
 *
 * @example getDay() // "29"
 * @example getDay() // "" (when system timeZone unavailable)
 */
export declare function getDay(): string;