Implement regex and POSIX pattern matching

[pbalduino]

Goal

Add regular expression support and POSIX pattern matching utilities.

Context

No regex support exists. Many tools (grep, sed, awk) require this.

Definition of Done

• [ ] regcomp() / regexec() / regfree() - POSIX regex
• [ ] regerror() - Error string conversion
• [ ] Extended regex support (REG_EXTENDED)
• [ ] fnmatch() - Filename pattern matching
• [ ] glob() / globfree() - Pathname expansion
• [ ] wordexp() / wordfree() - Shell-style word expansion

Dependencies

Required

• #193 - Minimal libc ✅

Priority

Medium - Needed for text processing tools

Estimated Time

10-14 weeks part-time

Notes

Consider using existing implementation (musl, TRE, PCRE)