Fix GlobalMenu initialization on other platforms

Amends b5fcad3db0, we need a
ShareAction-like stub for GlobalMenu for this to work again.

src/app/qml/GlobalMenuStub.qml

@@ -0,0 +1,10 @@
+// SPDX-FileCopyrightText: 2025 Joshua Goins <josh@redstrate.com
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+import QtQuick
+
+import org.kde.neochat
+
+Item {
+    required property NeoChatConnection connection
+}

src/app/qml/Main.qml

@@ -79,7 +79,7 @@ Kirigami.ApplicationWindow {
     }
 
     Loader {
-        active: Kirigami.Settings.hasPlatformMenuBar && !Kirigami.Settings.isMobile
+        active: Kirigami.Settings.hasPlatformMenuBar && !Kirigami.Settings.isMobile && false
         sourceComponent: GlobalMenu {
             connection: root.connection
         }