优化windows笔记功能

lib/widgets/app_shell.dart

@@ -0,0 +1,19 @@
+import 'dart:io';
+import 'package:flutter/material.dart';
+import 'custom_title_bar.dart';
+
+class AppShell extends StatelessWidget {
+  final Widget child;
+  const AppShell({super.key, required this.child});
+
+  @override
+  Widget build(BuildContext context) {
+    if (!Platform.isWindows) return child;
+    return Column(
+      children: [
+        const CustomTitleBar(),
+        Expanded(child: child),
+      ],
+    );
+  }
+}