Business-day math with real holiday calendars for FR, DE, GB, US, ES, IT, NL, BE (2025-2027, official sources — same datasets as /v1/holidays). Count working/weekend/holiday days in a date range (?from&to&country) or shift a date by N business days (?from&add=10&country). Weekend configurable (?weekend=fri,sat), optional ?region= for Länder/UK divisions. Holidays that suppress a working day are listed by name.