feat(ui): WebDAV 文件列表改用元数据标题/艺术家显示

之前列表只显示文件名，即使 DB 里已经有标签。
- SongDatabase 新增 getSongsByPaths()：一次批量按路径查（分块 400，避开变量上限）
- WebDAVFileListPage：
  * 加载目录后批量取元数据，title/artist 有值就替换文件名
  * 副标题显示 "艺术家 · 大小"，没有标签时仍显示大小
  * 监听 AudioService，正在播放的歌补全元数据后立即刷新对应行
  * 没有标签的新歌自然回退文件名，不影响使用

lib/database/song_database.dart

@@ -256,6 +256,33 @@ class SongDatabase {
     return result.isNotEmpty ? result.first : null;
   }
 
+  /// 批量按路径查元数据，返回 path -> row。
+  /// 文件列表页一次要显示几十上百首，逐条查会太慢。
+  Future<Map<String, Map<String, dynamic>>> getSongsByPaths(
+      List<String> paths) async {
+    final result = <String, Map<String, dynamic>>{};
+    if (paths.isEmpty) return result;
+
+    final db = await database;
+    const chunkSize = 400; // 避免 SQLite 变量数量上限
+    for (var i = 0; i < paths.length; i += chunkSize) {
+      final end = (i + chunkSize) > paths.length ? paths.length : i + chunkSize;
+      final slice = paths.sublist(i, end);
+      final placeholders = List.filled(slice.length, '?').join(',');
+      final rows = await db.query(
+        'songs',
+        where: 'remote_path IN ($placeholders)',
+        whereArgs: slice,
+      );
+      for (final row in rows) {
+        final path = row['remote_path'] as String?;
+        if (path != null) result[path] = row;
+      }
+    }
+    _logQuery('songs', 'getByPaths', args: {'count': result.length});
+    return result;
+  }
+
   Future<Map<String, dynamic>?> getSongByHash(String contentHash) async {
     _logQuery('songs', 'getByHash', args: {'content_hash': contentHash});
     final db = await database;

lib/pages/webdav_file_list_page.dart

@@ -4,6 +4,8 @@ import '../services/webdav_service.dart';
 import '../constants/ui_constants.dart';
 import '../base/base_state.dart';
 import '../controllers/playback_controller.dart';
+import '../database/song_database.dart';
+import '../services/audio_service.dart';
 
 class WebDAVFileListPage extends StatefulWidget {
   final String currentPath;
@@ -20,6 +22,10 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
   String _errorMessage = '';
   String _currentPath = '/';
 
+  /// 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;
+
   // 安全解码
   String _safeDecode(String input) {
     try {
@@ -33,9 +39,35 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
   void initState() {
     super.initState();
     _currentPath = widget.currentPath;
+    AudioService().addListener(_onPlaybackChanged);
     _loadDirectory();
   }
 
+  @override
+  void dispose() {
+    AudioService().removeListener(_onPlaybackChanged);
+    super.dispose();
+  }
+
+  /// 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;
+    if (path == null || path == _lastSyncedSongPath) return;
+    _lastSyncedSongPath = path;
+    _syncMetadataFor(path);
+  }
+
+  Future<void> _syncMetadataFor(String path) async {
+    if (!_items.any((item) => item.path == path)) return;
+    final row = await SongDatabase().getSongByPath(path);
+    if (row == null || !mounted) return;
+    final title = (row['title'] as String?)?.trim() ?? '';
+    if (title.isEmpty) return;
+    safeSetState(() {
+      _metaByPath = {..._metaByPath, path: row};
+    });
+  }
+
   // ============================================================
   // 加载目录
   // ============================================================
@@ -48,11 +80,28 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
     try {
       final items =
           await WebDAVService.instance.listDirectory(path: _currentPath);
+
+      // 一次性把本目录下所有文件的元数据查出来，列表直接用标签显示
+      final paths = items
+          .where((item) => !item.isDirectory)
+          .map((item) => item.path)
+          .toList();
+      var meta = <String, Map<String, dynamic>>{};
+      try {
+        meta = await SongDatabase().getSongsByPaths(paths);
+      } catch (e) {
+        debugPrint('⚠️ [WebDAVList] 批量读取元数据失败: $e');
+      }
+
       if (mounted) {
         safeSetState(() {
           _items = items;
+          _metaByPath = meta;
           _isLoading = false;
         });
+        // 如果当前正在播的歌就在这个目录里，补一次同步
+        _lastSyncedSongPath = null;
+        _onPlaybackChanged();
       }
     } catch (e) {
       if (mounted) {
@@ -295,6 +344,18 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
       final sizeStr = item.size != null
           ? '${(item.size! / 1024 / 1024).toStringAsFixed(1)} MB'
           : '';
+      // 有标签就用标签，没有才退回文件名（例如新歌尚未抓取元数据）
+      final meta = _metaByPath[item.path];
+      final metaTitle = (meta?['title'] as String?)?.trim() ?? '';
+      final metaArtist = (meta?['artist'] as String?)?.trim() ?? '';
+      final hasMeta = metaTitle.isNotEmpty;
+      final titleText = hasMeta ? metaTitle : displayName;
+      final subtitleText = [
+        if (hasMeta && metaArtist.isNotEmpty && metaArtist != '未知艺术家')
+          metaArtist,
+        if (sizeStr.isNotEmpty) sizeStr,
+      ].join(' · ');
+
       return ListTile(
         contentPadding: const EdgeInsets.symmetric(horizontal: 4, vertical: 2),
         leading: const Icon(
@@ -303,7 +364,7 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
           size: 28,
         ),
         title: Text(
-          displayName,
+          titleText,
           style: const TextStyle(
             fontSize: 16,
             fontWeight: FontWeight.w400,
@@ -313,7 +374,7 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
           overflow: TextOverflow.ellipsis,
         ),
         subtitle: Text(
-          sizeStr,
+          subtitleText,
           style: TextStyle(
             fontSize: 12,
             color: Colors.grey[500],