Replace legacy PCRE (libpcre3) with PCRE2 (libpcre2-8). PCRE1 has been
end-of-life since 2021.
- src/rule.h: use pcre2_code and pcre2_match_data types
- src/rule.c: pcre_compile -> pcre2_compile, pcre_exec -> pcre2_match,
pcre_free -> pcre2_code_free, with proper error message retrieval
- cmake/FindPCRE.cmake -> cmake/FindPCRE2.cmake: find libpcre2-8 via
pkg-config, pcre2-config, or manual search
- Update all CMakeLists.txt, config.h.cmake, configure.cmake, README.md
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
