部分界面调整，把底部的播放控件完整前置

lib/services/playback_service.dart

@@ -1,57 +1,91 @@
 // lib/services/playback_service.dart
 import 'package:media_kit/media_kit.dart';
 
+// ============================================================
+// PlaybackService - 播放引擎封装
+// 职责：管理 Player 生命周期，不涉及业务逻辑
+// ============================================================
 class PlaybackService {
-  static final PlaybackService _instance = PlaybackService._();
+  static final PlaybackService _instance = PlaybackService._internal();
   factory PlaybackService() => _instance;
-  PlaybackService._();
+  PlaybackService._internal();
 
-  late final Player _player;
+  Player? _player;
   bool _initialized = false;
 
-  // 获取 Player 实例（供 AudioService 直接监听）
+  // ---------- Getter ----------
   Player get player {
     if (!_initialized) init();
-    return _player;
+    return _player!;
   }
 
+  bool get isInitialized => _initialized;
+
+  // ---------- 初始化 ----------
   void init() {
     if (_initialized) return;
     _player = Player();
     _initialized = true;
+
+    // 可以在这里配置初始参数
+    // _player.setVolume(1.0);
   }
 
+  // ---------- 播放 ----------
   Future<void> play(String url, {Map<String, String>? headers}) async {
     if (!_initialized) init();
-    print('🎵 播放 URL: $url');
-    print('📋 认证头: ${headers?.keys}');
-    final media = headers != null && headers.isNotEmpty
+
+    final media = (headers != null && headers.isNotEmpty)
         ? Media(url, httpHeaders: headers)
         : Media(url);
-    await _player.open(media);
-    await _player.play();
+
+    await _player!.open(media);
+    await _player!.play();
   }
 
+  // ---------- 控制 ----------
   void pause() {
-    if (_initialized) _player.pause();
+    if (_initialized && _player != null) {
+      _player!.pause();
+    }
   }
 
   void resume() {
-    if (_initialized) _player.play();
+    if (_initialized && _player != null) {
+      _player!.play();
+    }
   }
 
   void stop() {
-    if (_initialized) _player.stop();
+    if (_initialized && _player != null) {
+      _player!.stop();
+    }
   }
 
   void seek(Duration position) {
-    if (_initialized) _player.seek(position);
+    if (_initialized && _player != null) {
+      _player!.seek(position);
+    }
   }
 
+  void setVolume(double volume) {
+    if (_initialized && _player != null) {
+      _player!.setVolume(volume);
+    }
+  }
+
+  // ---------- 释放 ----------
   void dispose() {
-    if (_initialized) {
-      _player.dispose();
+    if (_initialized && _player != null) {
+      _player!.dispose();
+      _player = null;
       _initialized = false;
     }
   }
+
+  // ---------- 重新初始化（用于 Hot Restart 场景） ----------
+  void reinitialize() {
+    dispose();
+    init();
+  }
 }