/**
 * Return the day of week (1-7) for a given ISO 8601 datetime string.
 *
 * - Monday=1 through Sunday=7.
 * - Returns null for invalid input.
 *
 * @param value ISO datetime string
 * @returns Day of week (1-7) or null on invalid input
 *
 * @example parseDayOfWeekFromDateTime("2024-01-01T12:00:00") // 1 (Monday)
 * @example parseDayOfWeekFromDateTime("2024-01-07T00:00:00") // 7 (Sunday)
 * @example parseDayOfWeekFromDateTime("invalid") // null
 */
export declare function parseDayOfWeekFromDateTime(value: string): number | null;