function addMonthsIso addMonthsIso(fromIso: string,months: number): string Add N months to an ISO timestamp, clamping to the last day of the target month. e.g. 2026-01-31 + 1mo → 2026-02-28 Preserves the time component (hour/minute/second/ms). Zero months returns the input with canonical ISO string formatting. Parameters fromIso: string months: number Return Type string