- Add sophisticated file preservation functionality to _clean_output_dir()
- Support .qsgen3_preserve file with shell glob patterns for selective preservation
- Preserve shared articles and important files during site regeneration
- Maintain backward compatibility (no preserve file = complete cleaning)
- Add comprehensive documentation in how-it-works.md
- Include example preserve file (.qsgen3_preserve.example)
- Remove legacy images directory and update documentation
- Fix workflow documentation formatting issues
