fix: remove dark backgrounds causing black rectangles

- PageLoader: remove bg-dark-950, use transparent background
- AdminLayout: remove motion animations
- Now lazy-loaded pages show Aurora background during loading

src/components/common/PageLoader.tsx

@@ -3,11 +3,10 @@ interface PageLoaderProps {
 }
 
 export default function PageLoader({ variant = 'dark' }: PageLoaderProps) {
-  const bgClass = variant === 'dark' ? 'bg-dark-950' : 'bg-gray-50';
   const spinnerColor = variant === 'dark' ? 'border-accent-500' : 'border-blue-500';
 
   return (
-    <div className={`flex min-h-screen items-center justify-center ${bgClass}`}>
+    <div className="flex min-h-[50vh] items-center justify-center">
       <div
         className={`h-10 w-10 border-[3px] ${spinnerColor} animate-spin rounded-full border-t-transparent`}
       />