Introduces an explicit GTK desktop portal portal entry so the session can expose standard portals (file chooser, app chooser, printing, notifications, etc.) to GNOME/Hyprland environments.
Also includes a minor formatting/syntax adjustment in the default Nix file to align the file structure.
Adds the GSettings schema directory path so runtime lookups can find desktop schemas, and includes the gsettings-desktop-schemas package to provide the necessary schemas. This ensures GTK/Qt applications and theming work correctly under Hyprland by enabling proper GSettings/gtk portal support.
elwrcl