style: [items] StatCards 6개 이상일 때 한 행에 모두 표시

- count >= 6일 때 md:grid-cols-6 적용
- 품목관리 화면에서 6개 카드가 한 행에 표시되도록 개선

src/components/organisms/StatCards.tsx

@@ -24,9 +24,11 @@ interface StatCardsProps {
 export function StatCards({ stats }: StatCardsProps) {
   const count = stats.length;
   const gridClass =
-    count >= 5
-      ? 'grid grid-cols-2 sm:grid-cols-3 md:grid-cols-5 gap-2'
-      : 'grid grid-cols-2 sm:grid-cols-3 md:grid-cols-4 gap-2';
+    count >= 6
+      ? 'grid grid-cols-2 sm:grid-cols-3 md:grid-cols-6 gap-2'
+      : count >= 5
+        ? 'grid grid-cols-2 sm:grid-cols-3 md:grid-cols-5 gap-2'
+        : 'grid grid-cols-2 sm:grid-cols-3 md:grid-cols-4 gap-2';
 
   return (
     <div className={gridClass}>