/**
 * Return a localized string for a PlainDateTime ISO input using Intl options.
 *
 * - Uses Temporal.PlainDateTime.toLocaleString for formatting.
 * - Accepts optional BCP 47 locale and Intl.DateTimeFormatOptions.
 * - Returns "" for invalid input.
 *
 * @param value ISO PlainDateTime string
 * @param locale optional BCP 47 locale identifier
 * @param options optional Intl.DateTimeFormatOptions
 * @returns localized date-time string or "" on invalid input
 *
 * @example formatDateTime("2024-03-15T14:30:00", "en-US", { dateStyle: "medium", timeStyle: "short" }) // "Mar 15, 2024 at 2:30 PM"
 * @example formatDateTime("2024-03-15T14:30:00", "de-DE", { dateStyle: "medium", timeStyle: "short" }) // "15.03.2024, 14:30"
 * @example formatDateTime("invalid") // ""
 */
export declare function formatDateTime(value: string, locale?: string, options?: Intl.DateTimeFormatOptions): string;