SumanTwati/bs-date-picker-react — reverse-engineered prompt

Build me a reusable React date picker component for Nepali Bikram Sambat dates that also works with normal Gregorian dates. I want it to feel polished and easy to drop into another app, with a popover calendar UI, month and year navigation, and the ability to switch between BS and AD views while keeping the selected date mapped correctly in both systems.

It should support Nepali and English display, show Nepali numerals for BS mode and English numerals for AD mode, and let me choose common output formats like YYYY MM DD, DD MM YYYY, and month name formats. The component should accept a default value, a language option, and an onDateChange callback that returns the selected date in both calendar formats.

Please make the styling responsive and clean, include the basic CSS needed for the component, and keep the background working nicely with light and dark themes. If anything about Nepali date conversion needs validation, look up the current docs online and wire it up properly.