/**
 * Return the hour (00-23) for a given ISO 8601 datetime string.
 *
 * - Returns zero-padded string for hour.
 * - Returns "" for invalid input.
 *
 * @param value ISO datetime string
 * @returns Hour (00-23) or "" on invalid input
 *
 * @example parseHourFromDateTime("2024-03-15T14:30:00") // "14"
 * @example parseHourFromDateTime("2024-03-15T00:00:00") // "00"
 * @example parseHourFromDateTime("invalid") // ""
 */
export declare function parseHourFromDateTime(value: string): string;