Add dev/debug startup flow and launch profiles

Handle design-time initialization and add a developer debug startup path: App now skips normal startup when in design mode and shows a DevDebugWindow when running in debug (unless a preview or apply-update command). CommandContext.IsDebugMode is extended to include DOTNET_ENVIRONMENT=Development via a new IsDevelopmentEnvironment helper. Program.Main and BuildAvaloniaApp are made public to aid tooling. Added multiple launchSettings profiles for debug and preview commands that set DOTNET_ENVIRONMENT=Development to simplify IDE debugging and UI previewing.

LanMountainDesktop.Launcher/App.axaml.cs

@@ -18,6 +18,12 @@ public partial class App : Application
 {
     public override void Initialize()
     {
+        if (Design.IsDesignMode)
+        {
+            AvaloniaXamlLoader.Load(this);
+            return;
+        }
+
         Logger.Initialize();
         var context = LauncherRuntimeContext.Current;
         var execution = LauncherExecutionContext.Capture();
@@ -32,6 +38,12 @@ public partial class App : Application
 
     public override void OnFrameworkInitializationCompleted()
     {
+        if (Design.IsDesignMode)
+        {
+            base.OnFrameworkInitializationCompleted();
+            return;
+        }
+
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
             desktop.ShutdownMode = ShutdownMode.OnExplicitShutdown;
@@ -49,6 +61,18 @@ public partial class App : Application
                 return;
             }
 
+            // 调试模式：只显示 DevDebugWindow，不走正常启动流程
+            // 避免启动主程序后 Launcher 自动退出，导致开发者无法预览 UI
+            if (context.IsDebugMode && !context.IsPreviewCommand &&
+                !string.Equals(context.Command, "apply-update", StringComparison.OrdinalIgnoreCase))
+            {
+                Logger.Info("Debug mode active — showing DevDebugWindow instead of normal launch flow.");
+                var devDebugWindow = new DevDebugWindow();
+                devDebugWindow.Show();
+                base.OnFrameworkInitializationCompleted();
+                return;
+            }
+
             if (string.Equals(context.Command, "apply-update", StringComparison.OrdinalIgnoreCase))
             {
                 var updateWindow = new UpdateWindow();