refactor: split desktop & mobile

flutter/lib/desktop/pages/desktop_home_page.dart

@@ -0,0 +1,15 @@
+import 'package:flutter/material.dart';
+
+class DesktopHomePage extends StatefulWidget {
+  DesktopHomePage({Key? key}) : super(key: key);
+
+  @override
+  State<StatefulWidget> createState() => _DesktopHomePageState();
+}
+
+class _DesktopHomePageState extends State<DesktopHomePage> {
+  @override
+  Widget build(BuildContext context) {
+    return Text("Hello Desktop");
+  }
+}