재고 상세 다이얼로그화 및 마스터 레이아웃 개선

lib/widgets/components/page_header.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/material.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
 
+import 'responsive_section.dart';
+
 /// 페이지 상단 타이틀/설명/액션을 일관되게 출력하는 헤더.
 class PageHeader extends StatelessWidget {
   const PageHeader({
@@ -22,27 +24,52 @@ class PageHeader extends StatelessWidget {
   Widget build(BuildContext context) {
     final theme = ShadTheme.of(context);
 
-    return Row(
-      crossAxisAlignment: CrossAxisAlignment.start,
-      children: [
-        if (leading != null) ...[leading!, const SizedBox(width: 16)],
-        Expanded(
-          child: Column(
-            crossAxisAlignment: CrossAxisAlignment.start,
-            children: [
-              Text(title, style: theme.textTheme.h2),
-              if (subtitle != null) ...[
-                const SizedBox(height: 6),
-                Text(subtitle!, style: theme.textTheme.muted),
+    final actionWidgets = actions ?? const <Widget>[];
+
+    final trailingSection = (actionWidgets.isEmpty && trailing == null)
+        ? const SizedBox.shrink()
+        : Align(
+            alignment: Alignment.centerRight,
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.end,
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                if (actionWidgets.isNotEmpty)
+                  Wrap(
+                    spacing: 12,
+                    runSpacing: 12,
+                    alignment: WrapAlignment.end,
+                    children: actionWidgets,
+                  ),
+                if (actionWidgets.isNotEmpty && trailing != null)
+                  const SizedBox(height: 12),
+                if (trailing != null) trailing!,
               ],
-            ],
+            ),
+          );
+
+    return ResponsiveStackedRow(
+      breakpoint: 640,
+      gap: 12,
+      leading: Row(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          if (leading != null) ...[leading!, const SizedBox(width: 16)],
+          Flexible(
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(title, style: theme.textTheme.h2),
+                if (subtitle != null) ...[
+                  const SizedBox(height: 6),
+                  Text(subtitle!, style: theme.textTheme.muted),
+                ],
+              ],
+            ),
           ),
-        ),
-        if (actions != null && actions!.isNotEmpty) ...[
-          Wrap(spacing: 12, runSpacing: 12, children: actions!),
         ],
-        if (trailing != null) ...[const SizedBox(width: 16), trailing!],
-      ],
+      ),
+      trailing: trailingSection,
     );
   }
 }