Implement locale and internationalization support

[pbalduino]

Goal

Add POSIX locale support for internationalized applications.

Context

No locale support exists. Most programs assume "C" locale.

Definition of Done

• [ ] setlocale() - Set locale
• [ ] localeconv() - Get numeric formatting conventions
• [ ] nl_langinfo() - Query locale information
• [ ] strcoll() / strxfrm() - Locale-aware string comparison
• [ ] Message catalogs (catopen/catgets/catclose)
• [ ] Locale data files

Dependencies

Required

• #193 - Minimal libc ✅

Priority

Low - Nice to have

Estimated Time

8-10 weeks part-time