Fix dialog rounded corners on mobile

The dialog's rounded corners were not displaying correctly on mobile devices, while they were fine on desktop. This commit addresses the issue.

src/hooks/use-mobile.tsx

@@ -4,11 +4,22 @@ import * as React from "react"
 const MOBILE_BREAKPOINT = 768
 
 export function useIsMobile() {
-  const [isMobile, setIsMobile] = React.useState<boolean>(false)
+  const [isMobile, setIsMobile] = React.useState<boolean>(
+    typeof window !== 'undefined' ? window.innerWidth < MOBILE_BREAKPOINT : false
+  )
 
   React.useEffect(() => {
+    if (typeof window === 'undefined') return;
+    
     const checkMobile = () => {
       setIsMobile(window.innerWidth < MOBILE_BREAKPOINT)
+      
+      // 모바일 화면인 경우 body에 클래스 추가
+      if (window.innerWidth < MOBILE_BREAKPOINT) {
+        document.body.classList.add('is-mobile');
+      } else {
+        document.body.classList.remove('is-mobile');
+      }
     }
     
     // 초기 확인