feat: new ui (#1455)

ui/flutter/windows/runner/flutter_window.cpp

@@ -27,8 +27,9 @@ bool FlutterWindow::OnCreate() {
   RegisterPlugins(flutter_controller_->engine());
   SetChildContent(flutter_controller_->view()->GetNativeWindow());
 
-  flutter_controller_->engine()->SetNextFrameCallback([&]() {
-  });
+  // Dart's window_manager bootstrap decides whether the main window should be
+  // shown. This preserves --hidden startup for tray/autostart launches.
+  flutter_controller_->engine()->SetNextFrameCallback([&]() {});
 
   // Flutter can complete the first frame before the "show window" callback is
   // registered. The following call ensures a frame is pending to ensure the