refactor(parser): add handler registry

[stacknil]

Summary

• split parser internals into timestamp, source-envelope, program-dispatch, program-handler, and failure-classifier modules
• add a typed handler registry result carrying match state, normalized event, failure category, and reason
• preserve AuthLogParser as the public interface and add registry/CRLF regression coverage
• document the internal parsing pipeline without changing the parser contract

Validation

• Windows: cmake -S . -B build, cmake --build build --config Debug, ctest --test-dir build -C Debug --output-on-failure
• Linux (WSL clean build): configure, build, and full CTest, 5/5 passed
• git diff --check
• local Markdown link check
• privacy and secret-pattern scan