Enables GSettings schemas for Hyprland

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.

nixos/desktop/window-managers/hyprland.nix

@@ -28,5 +28,6 @@
       "/home/elars/.nix-profile/share"
     ];
     GTK_USE_PORTAL = "1";
+    GSETTINGS_SCHEMA_DIR = "${pkgs.gsettings-desktop-schemas}/share/gsettings-schemas/${pkgs.gsettings-desktop-schemas.name}/glib-2.0/schemas";
   };
 }