docs: update README and add CHANGELOG for production-ready status

Update documentation to reflect completion of Phases 1-5:
- Add CHANGELOG.md documenting project history and achievements
- Update README.md with actual performance metrics (16-6,578x improvements)
- Document production-ready status with 314 passing tests
- Clarify Phase 6 as optional (current performance exceeds all targets)

All documentation now accurately reflects the state of the codebase.

Author: bug-ops