- main.py: wrap _ensure_display_access() in sys.platform != "win32" check
- main.py: add FileNotFoundError to except in _find_active_xauthority()
- claude_setup.py: platform-aware error message for ssh-keygen not found
- CLAUDE.md: add mandatory cross-platform rules for all contributors
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>