fix(theme): clearer naming and making secondary optional

hosts/bunk/settings.nix

@@ -36,7 +36,7 @@
     theme = {
       background = {
         lockscreen = "wallpaper_2";
-        desktop = "wallpaper_1";
+        primary = "wallpaper_1";
       };
     };
   };

hosts/kima/settings.nix

@@ -36,8 +36,8 @@
     theme = {
       background = {
         lockscreen = "wallpaper_4";
-        desktop = "wallpaper_1";
-        vertical = "wallpaper_5";
+        primary = "wallpaper_1";
+        secondary = "wallpaper_5";
       };
     };
   };

hosts/toothpc/settings.nix

@@ -23,7 +23,7 @@
     theme = {
       background = {
         lockscreen = "wallpaper_2";
-        desktop = "wallpaper_1";
+        primary = "wallpaper_1";
       };
     };
   };

modules/settings/theme/default.nix

@@ -18,14 +18,14 @@ in
         apply = name: bgs.${name};
         example = "wallpaper_1";
       };
-      desktop = mkOption {
+      primary = mkOption {
         type = types.enum bgList;
         apply = name: bgs.${name};
         example = "wallpaper_2";
       };
-      vertical = mkOption {
+      secondary = mkOption {
         type = types.enum bgList;
-        apply = name: bgs.${name};
+        apply = name: if name == null then null else bgs.${name};
         example = "wallpaper_3";
       };
     };