feat(ui): 播放页改为三页横向切换（信息 / 主页 / 歌词）

- PageView 三页：左=文件信息，中=播放主页，右=歌词
- 顶部指示器：两点+连线，左点亮=信息页，右点亮=歌词页，
  中间都暗=主页；点圆点可直接跳转
- 文件信息页：标题/歌手/专辑/文件夹/文件名/格式/路径，
  优先用 DB 元数据，路径与文件名做解码
- 歌词页：占位（暂无歌词 + 歌名）

真机验证：慢速左右滑动切换正常，指示器跟随。

lib/pages/player_page.dart

@@ -26,8 +26,20 @@ class _PlayerPageState extends BaseState<PlayerPage> {
   bool _isFavorite = false;
   String _album = '';
   String _folder = '';
+  String _dbTitle = '';
+  String _dbArtist = '';
   String? _metaSongId;
 
+  /// 0 = 文件信息，1 = 播放主页，2 = 歌词
+  final PageController _pageController = PageController(initialPage: 1);
+  int _pageIndex = 1;
+
+  @override
+  void dispose() {
+    _pageController.dispose();
+    super.dispose();
+  }
+
   String _formatDuration(Duration d) {
     if (d.inMilliseconds < 0) return '00:00';
     final minutes = d.inMinutes;
@@ -88,10 +100,14 @@ class _PlayerPageState extends BaseState<PlayerPage> {
 
     final db = SongDatabase();
     String album = '';
+    String dbTitle = '';
+    String dbArtist = '';
     bool favorite = false;
     try {
       final row = await db.getSongByPath(song.id);
       album = (row?['album'] as String?)?.trim() ?? '';
+      dbTitle = (row?['title'] as String?)?.trim() ?? '';
+      dbArtist = (row?['artist'] as String?)?.trim() ?? '';
       favorite = await db.isFavorite(song.id);
     } catch (_) {
       // 元数据只是装饰，失败忽略
@@ -113,6 +129,8 @@ class _PlayerPageState extends BaseState<PlayerPage> {
     setState(() {
       _album = album;
       _folder = folder;
+      _dbTitle = dbTitle;
+      _dbArtist = dbArtist;
       _isFavorite = favorite;
     });
   }
@@ -175,6 +193,7 @@ class _PlayerPageState extends BaseState<PlayerPage> {
           icon: const Icon(Icons.keyboard_arrow_down, color: Colors.white70),
           onPressed: _closePage,
         ),
+        title: _buildPageIndicator(),
         actions: [
           PopupMenuButton<String>(
             icon: const Icon(Icons.more_vert, color: Colors.white54),
@@ -230,8 +249,57 @@ class _PlayerPageState extends BaseState<PlayerPage> {
           ),
         ],
       ),
-      body: SafeArea(
+      body: PageView(
-        child: Padding(
+        controller: _pageController,
+        onPageChanged: (index) => setState(() => _pageIndex = index),
+        children: [
+          _buildInfoPage(song),
+          _buildMainPage(service, song, isPlaying),
+          _buildLyricsPage(song),
+        ],
+      ),
+    );
+  }
+
+  /// 顶部两点指示器：左点=信息页，右点=歌词页，中间不亮表示在主页
+  Widget _buildPageIndicator() {
+    Widget dot(int index) {
+      final active = _pageIndex == index;
+      return GestureDetector(
+        onTap: () => _pageController.animateToPage(
+          index,
+          duration: const Duration(milliseconds: 280),
+          curve: Curves.easeOutCubic,
+        ),
+        child: AnimatedContainer(
+          duration: const Duration(milliseconds: 200),
+          width: 7,
+          height: 7,
+          decoration: BoxDecoration(
+            shape: BoxShape.circle,
+            color: active ? Colors.white : Colors.white24,
+          ),
+        ),
+      );
+    }
+
+    return Row(
+      mainAxisSize: MainAxisSize.min,
+      children: [
+        dot(0),
+        Container(
+          width: 56,
+          height: 1,
+          margin: const EdgeInsets.symmetric(horizontal: 8),
+          color: Colors.white12,
+        ),
+        dot(2),
+      ],
+    );
+  }
+
+  Widget _buildMainPage(AudioService service, Song song, bool isPlaying) {
+    return Padding(
       padding: const EdgeInsets.symmetric(horizontal: 24),
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.start,
@@ -317,8 +385,97 @@ class _PlayerPageState extends BaseState<PlayerPage> {
           const SizedBox(height: 20),
         ],
       ),
+    );
+  }
+
+  /// 左页：文件信息
+  Widget _buildInfoPage(Song song) {
+    final rawName = song.id.split('/').last;
+    String fileName = rawName;
+    try {
+      fileName = Uri.decodeComponent(rawName);
+    } catch (_) {}
+
+    final dot = fileName.lastIndexOf('.');
+    final format =
+        dot > 0 ? fileName.substring(dot + 1).toUpperCase() : '未知';
+
+    String decodedPath = song.id;
+    try {
+      decodedPath = Uri.decodeComponent(song.id);
+    } catch (_) {}
+
+    final effectiveArtist = _dbArtist.isNotEmpty
+        ? _dbArtist
+        : (song.artist.isEmpty ? '未知' : song.artist);
+    final effectiveTitle = _dbTitle.isNotEmpty ? _dbTitle : song.title;
+
+    final rows = <MapEntry<String, String>>[
+      MapEntry('标题', effectiveTitle),
+      MapEntry('歌手', effectiveArtist),
+      MapEntry('专辑', _album.isEmpty ? '未知' : _album),
+      MapEntry('文件夹', _folder.isEmpty ? '根目录' : _folder),
+      MapEntry('文件名', fileName),
+      MapEntry('格式', format),
+      MapEntry('路径', decodedPath),
+    ];
+
+    return SingleChildScrollView(
+      padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 8),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          const Text(
+            '文件信息',
+            style: TextStyle(
+              fontSize: 18,
+              fontWeight: FontWeight.w600,
+              color: Colors.white,
             ),
           ),
+          const SizedBox(height: 20),
+          for (final row in rows) ...[
+            Text(
+              row.key,
+              style: TextStyle(fontSize: 12, color: Colors.grey[600]),
+            ),
+            const SizedBox(height: 4),
+            Text(
+              row.value,
+              style: const TextStyle(
+                fontSize: 14,
+                color: Colors.white,
+                height: 1.4,
+              ),
+            ),
+            const SizedBox(height: 18),
+          ],
+        ],
+      ),
+    );
+  }
+
+  /// 右页：歌词（占位）
+  Widget _buildLyricsPage(Song song) {
+    return Center(
+      child: Column(
+        mainAxisAlignment: MainAxisAlignment.center,
+        children: [
+          Icon(Icons.lyrics_outlined, size: 44, color: Colors.grey[700]),
+          const SizedBox(height: 14),
+          Text(
+            '暂无歌词',
+            style: TextStyle(fontSize: 14, color: Colors.grey[600]),
+          ),
+          const SizedBox(height: 6),
+          Text(
+            song.title,
+            style: TextStyle(fontSize: 12, color: Colors.grey[700]),
+            maxLines: 1,
+            overflow: TextOverflow.ellipsis,
+          ),
+        ],
+      ),
     );
   }