메인 배너 진열을 grid 레이아웃으로 변경 (모바일 2열 / 태블릿 3열 / 데스크톱 6열 1행)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Views/Home/Index.cshtml

@@ -40,7 +40,7 @@
 
     <br/>
 
-    <div class="columns-2 sm:columns-3 lg:columns-6 gap-2 mb-2">
+    <div class="grid grid-cols-2 sm:grid-cols-3 lg:grid-cols-6 gap-2 mb-2">
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