style(ad): 네이티브 광고 라운드 제거

lib/presentation/widgets/native_ad_placeholder.dart

@@ -111,7 +111,7 @@ class _NativeAdPlaceholderState extends State<NativeAdPlaceholder> {
     return NativeTemplateStyle(
       templateType: TemplateType.medium,
       mainBackgroundColor: isDark ? AppColors.darkSurface : Colors.white,
-      cornerRadius: 12,
+      cornerRadius: 0,
       callToActionTextStyle: NativeTemplateTextStyle(
         textColor: Colors.white,
         backgroundColor: AppColors.lightPrimary,
@@ -152,10 +152,7 @@ class _NativeAdPlaceholderState extends State<NativeAdPlaceholder> {
       height: containerHeight,
       width: double.infinity,
       decoration: _decoration(isDark),
-      child: ClipRRect(
-        borderRadius: BorderRadius.circular(10),
-        child: AdWidget(ad: _nativeAd!),
-      ),
+      child: AdWidget(ad: _nativeAd!),
     );
   }
 
@@ -187,7 +184,6 @@ class _NativeAdPlaceholderState extends State<NativeAdPlaceholder> {
   BoxDecoration _decoration(bool isDark) {
     return BoxDecoration(
       color: isDark ? AppColors.darkSurface : Colors.white,
-      borderRadius: BorderRadius.circular(12),
       border: Border.all(
         color: isDark ? AppColors.darkDivider : AppColors.lightDivider,
         width: 2,