Version 1.2.0

Major Features:
- Automatic Python default setting with --set-default flag
- New set-default command for Python version management
- Complete Python installation with venv and distutils
- Smart update-alternatives configuration

Bug Fixes:
- Fixed non-Anaconda user Python PATH issues
- Removed hardcoded version references
- Better installation verification

See CHANGELOG.md and FIX_EXPLANATION.md for full details.