Set default wallpaper to Attack-on-Titan-2

- Updated host variables files to select Attack-on-Titan-2.jpg and added
  rating comments.
- Simplified boot.nix by removing host‑specific imports and configuring
  limine via package, resolution, and branding color.
- Added limine target support in stylix with color, image, and tile
  scaling options.
- Removed the unused noctalia colors module and its import.
- Adjusted noctalia wallpaper settings to use config.stylix.image
  instead of a host import.

modules/core/stylix.nix

@@ -36,5 +36,14 @@ in {
         popups = 12;
       };
     };
+    targets.limine = {
+      enable = true;
+      colors.enable = true;
+      image.enable = true;
+      imageScalingMode = {
+        enable = true;
+        override = "tile";
+      };
+    };
   };
 }