页面层级与返回逻辑实现完成，并且去掉web相关代码支持

lib/pages/playlist_page.dart

@@ -1,15 +1,9 @@
-// lib/pages/playlist_page.dart
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import '../services/audio_service.dart';
 
 class PlaylistPage extends StatelessWidget {
-  final VoidCallback onClose;
-
-  const PlaylistPage({
-    super.key,
-    required this.onClose,
-  });
+  const PlaylistPage({super.key});
 
   @override
   Widget build(BuildContext context) {
@@ -33,7 +27,7 @@ class PlaylistPage extends StatelessWidget {
         foregroundColor: Colors.white,
         leading: IconButton(
           icon: const Icon(Icons.arrow_back_ios_new),
-          onPressed: onClose,
+          onPressed: () => Navigator.pop(context),
         ),
         actions: [
           IconButton(
@@ -60,7 +54,7 @@ class PlaylistPage extends StatelessWidget {
                       onPressed: () {
                         service.clearQueue();
                         Navigator.pop(context);
-                        onClose();
+                        Navigator.pop(context);
                       },
                       child: const Text(
                         '清空',
@@ -146,7 +140,7 @@ class PlaylistPage extends StatelessWidget {
                       : null,
                   onTap: () {
                     service.setQueue(queue, startIndex: index);
-                    onClose();
+                    Navigator.pop(context);
                   },
                 );
               },