- Add gsettings-desktop-schemas for GNOME schema support on non-GNOME systems
- Add libstdc++.so.6 support via stdenv.cc.cc.lib for Python packages
- Include all required system libraries for Python virtual environment
- Set XDG_DATA_DIRS to include GNOME schemas path
- Reorganize Python environment configuration for better clarity
This resolves the issue where Light mode couldn't be selected in the
quickshell settings menu due to missing dependencies and library linking issues.