Improved Japanese localization for date formatting

We fixed several date formatting issues for the Japanese locale (lang=ja). Date pickers now show plain numeric dates without ordinal suffixes, matching standard Japanese calendar conventions. All other date surfaces, including overview pages, booking summaries, confirmations, and emails, now use proper Japanese suffixes (年 / 月 / 日).

Full dates with day of week follow the standard [M]月 [D]日 ([曜日]) format. The lang parameter is now correctly respected on custom domains as well.