refactor: 重构待办事项模块结构与命名

src/Hua.Todo.Maui/Platforms/Windows/MainPage.Windows.cs

@@ -1,4 +1,5 @@
 using Microsoft.Maui.Controls;
+using Microsoft.Maui.ApplicationModel;
 
 namespace Hua.Todo.Maui.Views
 {
@@ -30,5 +31,53 @@ namespace Hua.Todo.Maui.Views
             var windowService = new Platforms.Windows.WindowsWindowService();
             windowService.MinimizeWindow(window);
         }
+
+        partial void PlatformPrepareWebViewContainer()
+        {
+            if (Platforms.Windows.WebView2RuntimeDetector.IsRuntimeInstalled(out _))
+            {
+                return;
+            }
+
+            _isWebViewContainerReady = false;
+
+            var downloadUrl = "https://developer.microsoft.com/microsoft-edge/webview2/";
+            var content = new VerticalStackLayout
+            {
+                Padding = new Thickness(20),
+                Spacing = 12,
+                Children =
+                {
+                    new Label
+                    {
+                        Text = "检测到系统未安装 WebView2 Runtime，无法加载主界面。",
+                        FontSize = 16
+                    },
+                    new Label
+                    {
+                        Text = "请安装 Microsoft Edge WebView2 Runtime（Evergreen），安装完成后重新打开应用。",
+                        Opacity = 0.85
+                    },
+                    new Button
+                    {
+                        Text = "打开下载页面",
+                        Command = new Command(async () =>
+                        {
+                            await Launcher.Default.OpenAsync(downloadUrl);
+                        })
+                    },
+                    new Button
+                    {
+                        Text = "退出应用",
+                        Command = new Command(() =>
+                        {
+                            Microsoft.Maui.Controls.Application.Current?.Quit();
+                        })
+                    }
+                }
+            };
+
+            Content = new ScrollView { Content = content };
+        }
     }
 }