Rewrite Installation-and-Setup: add download methods, venv guide, fix running instructions
- Add four download methods: git clone, GitHub Desktop, ZIP download, single file download
- Add optional virtual environment setup section
- Add double-click in File Explorer as a run method
- Remove CATIA Macro Manager section (does not support Python)
- Renumber sections accordingly
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>