Fix centered layout for demo header

ui/README.md

@@ -70,6 +70,7 @@
 - 移除了 demo 中 `Accordion` 示例的固定高度，避免多项同时展开后内容文本被裁切和溢出
 - 微调了多行 `TextBox` 的水平文字内边距，让大尺寸编辑区中的光标和首行文本不会显得过于贴近左边框
 - 将 demo 顶部的 `msimeui` 标题和副标题改为居中展示，并把标题上方留白收窄到原来的一半
+- 修正了 demo 顶部标题区的居中方式：改为通过独立 header 容器居中内容，确保 `msimeui` 标题和描述文本在页面顶部真正水平居中
 
 ## 构建
 

ui/demos/msimeui-demo/DemoScene.cpp

@@ -10,15 +10,13 @@ std::unique_ptr<Scene> CreateDemoScene()
 {
     auto root = std::make_shared<StackPanel>(0.0f);
     root->AddChild(std::make_shared<Spacer>(14.0f));
-    auto appTitle = std::make_shared<TextBlock>(L"msimeui", 34.0f, D2D1::ColorF(0x111827), true);
-    appTitle->SetHorizontalAlignment(HorizontalAlignment::Center);
-    root->AddChild(appTitle);
-    root->AddChild(std::make_shared<Spacer>(12.0f));
-    auto appSubtitle =
+    auto appHeader = std::make_shared<StackPanel>(12.0f);
+    appHeader->SetHorizontalContentAlignment(HorizontalAlignment::Center);
+    appHeader->AddChild(std::make_shared<TextBlock>(L"msimeui", 34.0f, D2D1::ColorF(0x111827), true));
+    appHeader->AddChild(
         std::make_shared<TextBlock>(L"A retained-mode Win32 GUI framework with Direct2D / DirectWrite and in-tree TSF.",
-                                    16.0f, D2D1::ColorF(0x5B6472));
-    appSubtitle->SetHorizontalAlignment(HorizontalAlignment::Center);
-    root->AddChild(appSubtitle);
+                                    16.0f, D2D1::ColorF(0x5B6472)));
+    root->AddChild(appHeader);
     root->AddChild(std::make_shared<Spacer>(36.0f));
 
     Brush surface;