feat(search): WebDAV 文件夹内搜索

- 列表页右上角「全部播放」换成搜索（刷新保留）
- 新页面 WebDAVSearchPage：输入关键字实时过滤当前文件夹的歌曲
- 匹配范围：文件名、元数据标题、艺术家（大小写不敏感）
- 结果显示封面/标题/艺术家，点击从该首开始播放并返回列表
- 空状态分两种：未输入提示、无结果提示

真机验证：搜索 "forza" 命中 2 首，一条显示标签标题、一条显示文件名。

lib/pages/webdav_file_list_page.dart

@@ -10,6 +10,7 @@ import '../services/audio_service.dart';
 import '../services/metadata_events.dart';
 import '../widgets/song_artwork.dart';
 import '../widgets/add_to_playlist_sheet.dart';
+import 'webdav_search_page.dart';
 
 class WebDAVFileListPage extends StatefulWidget {
   final String currentPath;
@@ -278,9 +279,17 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
         ),
         actions: [
           IconButton(
-            icon: const Icon(Icons.playlist_play),
-            onPressed: _playAll,
-            tooltip: '全部播放',
+            icon: const Icon(Icons.search),
+            onPressed: () => Navigator.push(
+              context,
+              MaterialPageRoute(
+                builder: (_) => WebDAVSearchPage(
+                  directoryPath: _currentPath,
+                  items: _items,
+                ),
+              ),
+            ),
+            tooltip: '搜索本文件夹',
           ),
           IconButton(
             icon: const Icon(Icons.refresh),

lib/pages/webdav_search_page.dart

@@ -0,0 +1,215 @@
+// lib/pages/webdav_search_page.dart
+import 'package:flutter/material.dart';
+
+import '../controllers/playback_controller.dart';
+import '../database/song_database.dart';
+import '../services/webdav_service.dart';
+import '../widgets/song_artwork.dart';
+
+/// 在当前 WebDAV 文件夹内搜索歌曲
+class WebDAVSearchPage extends StatefulWidget {
+  final String directoryPath;
+  final List<WebDAVItem> items;
+
+  const WebDAVSearchPage({
+    super.key,
+    required this.directoryPath,
+    required this.items,
+  });
+
+  @override
+  State<WebDAVSearchPage> createState() => _WebDAVSearchPageState();
+}
+
+class _WebDAVSearchPageState extends State<WebDAVSearchPage> {
+  final TextEditingController _controller = TextEditingController();
+  final FocusNode _focusNode = FocusNode();
+
+  /// path -> songs 表行
+  Map<String, Map<String, dynamic>> _meta = {};
+  String _query = '';
+
+  List<WebDAVItem> get _files =>
+      widget.items.where((item) => !item.isDirectory).toList();
+
+  @override
+  void initState() {
+    super.initState();
+    _loadMeta();
+  }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    _focusNode.dispose();
+    super.dispose();
+  }
+
+  Future<void> _loadMeta() async {
+    try {
+      final paths = _files.map((item) => item.path).toList();
+      final meta = await SongDatabase().getSongsByPaths(paths);
+      if (!mounted) return;
+      setState(() => _meta = meta);
+    } catch (e) {
+      debugPrint('⚠️ [Search] 读取元数据失败: $e');
+    }
+  }
+
+  String _decode(String input) {
+    try {
+      return Uri.decodeComponent(input);
+    } catch (_) {
+      return input;
+    }
+  }
+
+  List<WebDAVItem> get _results {
+    final keyword = _query.trim().toLowerCase();
+    if (keyword.isEmpty) return const [];
+    return _files.where((item) {
+      final name = _decode(item.name).toLowerCase();
+      final meta = _meta[item.path];
+      final title = (meta?['title'] as String? ?? '').toLowerCase();
+      final artist = (meta?['artist'] as String? ?? '').toLowerCase();
+      return name.contains(keyword) ||
+          title.contains(keyword) ||
+          artist.contains(keyword);
+    }).toList();
+  }
+
+  Future<void> _play(WebDAVItem item) async {
+    try {
+      await PlaybackController().playFromWebDAV(
+        directoryPath: widget.directoryPath,
+        clickedSongPath: item.path,
+        allItems: widget.items,
+      );
+      if (mounted) Navigator.pop(context);
+    } catch (e) {
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text('播放失败: $e')),
+      );
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final results = _results;
+
+    return Scaffold(
+      backgroundColor: const Color(0xFF0E1211),
+      appBar: AppBar(
+        backgroundColor: Colors.transparent,
+        elevation: 0,
+        foregroundColor: Colors.white,
+        titleSpacing: 0,
+        title: TextField(
+          controller: _controller,
+          focusNode: _focusNode,
+          autofocus: true,
+          style: const TextStyle(color: Colors.white, fontSize: 16),
+          cursorColor: const Color(0xFFB8D4D0),
+          decoration: const InputDecoration(
+            hintText: '搜索本文件夹的歌曲',
+            hintStyle: TextStyle(color: Colors.white38, fontSize: 15),
+            border: InputBorder.none,
+          ),
+          onChanged: (value) => setState(() => _query = value),
+        ),
+        actions: [
+          if (_query.isNotEmpty)
+            IconButton(
+              icon: const Icon(Icons.close, color: Colors.white54),
+              tooltip: '清除',
+              onPressed: () {
+                _controller.clear();
+                setState(() => _query = '');
+              },
+            ),
+        ],
+      ),
+      body: _query.trim().isEmpty
+          ? _buildHint()
+          : results.isEmpty
+              ? _buildEmpty()
+              : ListView.builder(
+                  padding: const EdgeInsets.symmetric(
+                      horizontal: 16, vertical: 8),
+                  itemCount: results.length,
+                  itemBuilder: (context, index) {
+                    final item = results[index];
+                    final meta = _meta[item.path];
+                    final metaTitle =
+                        (meta?['title'] as String?)?.trim() ?? '';
+                    final metaArtist =
+                        (meta?['artist'] as String?)?.trim() ?? '';
+                    final artwork =
+                        (meta?['artwork_path'] as String?)?.trim() ?? '';
+                    final name = _decode(item.name);
+
+                    return ListTile(
+                      contentPadding:
+                          const EdgeInsets.symmetric(horizontal: 4),
+                      visualDensity: VisualDensity.compact,
+                      leading: SongArtwork(
+                        filePath: artwork.isNotEmpty ? artwork : null,
+                        size: 44,
+                        fallbackIcon: Icons.audiotrack,
+                      ),
+                      title: Text(
+                        metaTitle.isNotEmpty ? metaTitle : name,
+                        style: const TextStyle(
+                            color: Colors.white, fontSize: 16),
+                        maxLines: 1,
+                        overflow: TextOverflow.ellipsis,
+                      ),
+                      subtitle: Text(
+                        metaArtist.isNotEmpty
+                            ? metaArtist
+                            : (item.size != null
+                                ? '${(item.size! / 1024 / 1024).toStringAsFixed(1)} MB'
+                                : ''),
+                        style: const TextStyle(
+                            color: Colors.grey, fontSize: 12),
+                        maxLines: 1,
+                        overflow: TextOverflow.ellipsis,
+                      ),
+                      onTap: () => _play(item),
+                    );
+                  },
+                ),
+    );
+  }
+
+  Widget _buildHint() {
+    return Center(
+      child: Column(
+        mainAxisAlignment: MainAxisAlignment.center,
+        children: [
+          Icon(Icons.search, size: 48, color: Colors.grey[700]),
+          const SizedBox(height: 14),
+          Text(
+            '输入歌名、歌手或文件名',
+            style: TextStyle(color: Colors.grey[500], fontSize: 14),
+          ),
+          const SizedBox(height: 6),
+          Text(
+            '只在当前文件夹内搜索',
+            style: TextStyle(color: Colors.grey[700], fontSize: 12),
+          ),
+        ],
+      ),
+    );
+  }
+
+  Widget _buildEmpty() {
+    return Center(
+      child: Text(
+        '没有找到「${_query.trim()}」',
+        style: TextStyle(color: Colors.grey[500], fontSize: 14),
+      ),
+    );
+  }
+}