feat(metadata): 元数据补全后主动推送界面刷新

之前标签补全后，收藏/文件列表要退出重进才显示新信息。
- 新增 MetadataEvents 事件总线（MetadataUpdate: path + songs 行）
- MetadataService 写库成功后 publish
- 首页收藏列表订阅：按 path 替换对应 SongItem（标题/艺术家/封面）
- WebDAV 文件列表订阅：按 path 更新 _metaByPath

效果：歌曲播完标签抓取完成后，列表里的那一行自动变成标签信息，
不需要返回重进。

lib/metadata/metadata_service.dart

@@ -7,6 +7,7 @@ import 'metadata_model.dart';
 import 'metadata_reader.dart';
 import 'metadata_normalizer.dart';
 import 'metadata_stability.dart';
+import '../services/metadata_events.dart';
 import 'metadata_cache.dart';
 import 'file_provider.dart';
 import '../utils/artwork_helper.dart';
@@ -189,6 +190,9 @@ class MetadataService {
       await _db.updateSong(songKey, row);
     }
 
+    // 通知界面局部刷新（收藏/文件列表/歌单等）
+    MetadataEvents().publish(fileId, row);
+
     final merged = FinalMetadata(
       title: row['title'] as String? ?? '',
       artist: row['artist'] as String? ?? '',

lib/pages/home_page.dart

@@ -1,6 +1,8 @@
+import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import '../services/audio_service.dart';
+import '../services/metadata_events.dart';
 import '../services/webdav_service.dart';
 import '../widgets/magnetic_scroll_physics.dart';
 import 'webdav_setup_page.dart';
@@ -163,6 +165,7 @@ class _HomePageState extends BaseState<HomePage> {
   /// 0 = 我的收藏，1 = 歌单列表（左右滑动切换）
   int _homeTab = 0;
   final PageController _homePageController = PageController();
+  StreamSubscription<MetadataUpdate>? _metaSub;
   List<PlaylistSummary> _playlistSummaries = [];
 
   // ========== 滚动控制 ==========
@@ -240,6 +243,31 @@ class _HomePageState extends BaseState<HomePage> {
     }
   }
 
+  /// 元数据补全后，按 path 更新收藏列表里的对应行
+  void _onMetadataUpdate(MetadataUpdate update) {
+    final index = _favorites.indexWhere((item) => item.path == update.path);
+    if (index < 0 || !mounted) return;
+
+    final row = update.row;
+    final title = (row['title'] as String?)?.trim() ?? '';
+    final artist = (row['artist'] as String?)?.trim() ?? '';
+    final artwork = (row['artwork_path'] as String?)?.trim() ?? '';
+
+    final old = _favorites[index];
+    safeSetState(() {
+      _favorites[index] = SongItem(
+        path: old.path,
+        fileName: old.fileName,
+        title: title.isNotEmpty ? title : old.title,
+        artist: artist.isNotEmpty ? artist : old.artist,
+        artworkPath: artwork.isNotEmpty ? artwork : old.artworkPath,
+        sourceTag: old.sourceTag,
+        metadataState: (title.isNotEmpty || old.title != null)
+            ? 'success'
+            : 'unknown',
+      );
+    });
+  }
   void _onScroll() {
     if (mounted) safeSetState(() {});
   }

lib/pages/webdav_file_list_page.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 // lib/pages/webdav_file_list_page.dart
 import 'package:flutter/material.dart';
 import '../services/webdav_service.dart';
@@ -6,6 +7,7 @@ import '../base/base_state.dart';
 import '../controllers/playback_controller.dart';
 import '../database/song_database.dart';
 import '../services/audio_service.dart';
+import '../services/metadata_events.dart';
 import '../widgets/song_artwork.dart';
 import '../widgets/add_to_playlist_sheet.dart';
 
@@ -27,6 +29,7 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
   /// path -> 元数据行（songs 表），用于把文件名替换成标签里的标题/艺术家
   Map<String, Map<String, dynamic>> _metaByPath = {};
   String? _lastSyncedSongPath;
+  StreamSubscription<MetadataUpdate>? _metaSub;
 
   /// 已收藏的歌曲路径
   Set<String> _favoritePaths = {};
@@ -54,6 +57,14 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
     super.dispose();
   }
 
+  /// 元数据补全后，按 path 更新列表行的标题/艺术家/封面
+  void _onMetadataUpdate(MetadataUpdate update) {
+    if (!_items.any((item) => item.path == update.path)) return;
+    if (!mounted) return;
+    safeSetState(() {
+      _metaByPath = {..._metaByPath, update.path: update.row};
+    });
+  }
   /// 播放中的歌一旦补全了元数据，立刻刷新列表里对应的那一行
   void _onPlaybackChanged() {
     final path = AudioService().currentSong?.id;

lib/services/metadata_events.dart

@@ -0,0 +1,30 @@
+// lib/services/metadata_events.dart
+import 'dart:async';
+
+/// 一条元数据更新（path + songs 表的最新行）
+class MetadataUpdate {
+  final String path;
+  final Map<String, dynamic> row;
+
+  const MetadataUpdate(this.path, this.row);
+}
+
+/// 元数据更新事件总线。
+///
+/// 之前各列表页靠"返回时重查"来刷新，歌曲补全标签后要退出重进才看得到。
+/// 现在 MetadataService 写库成功后 publish，订阅的页面按 path 局部更新。
+class MetadataEvents {
+  static final MetadataEvents _instance = MetadataEvents._internal();
+  factory MetadataEvents() => _instance;
+  MetadataEvents._internal();
+
+  final StreamController<MetadataUpdate> _controller =
+      StreamController<MetadataUpdate>.broadcast();
+
+  Stream<MetadataUpdate> get stream => _controller.stream;
+
+  void publish(String path, Map<String, dynamic> row) {
+    if (path.isEmpty) return;
+    _controller.add(MetadataUpdate(path, row));
+  }
+}