style(ui): 列表行距收紧 + 收藏项显示封面

- 收藏列表：vertical padding 6 -> 2，ListTile 用 compact，
  标题 17->16、副标题 14->13，行高明显变紧凑
- 收藏项 leading 从音符图标换成 SongArtwork（复用 songs.artwork_path）
- WebDAV 文件列表：contentPadding 去掉 vertical 2，加 compact

真机截图确认：行距更接近设计稿，有元数据的歌显示封面。

lib/pages/home_page.dart

@@ -6,6 +6,7 @@ import '../widgets/magnetic_scroll_physics.dart';
 import 'webdav_setup_page.dart';
 import 'settings_page.dart';
 import '../database/song_database.dart';
+import '../widgets/song_artwork.dart';
 import 'webdav_file_list_page.dart';
 import '../constants/ui_constants.dart';
 import '../base/base_state.dart';
@@ -18,6 +19,7 @@ class SongItem {
   final String fileName;
   final String? title;
   final String? artist;
+  final String? artworkPath;
   final String sourceTag;
   final String metadataState;
 
@@ -26,6 +28,7 @@ class SongItem {
     required this.fileName,
     this.title,
     this.artist,
+    this.artworkPath,
     required this.sourceTag,
     this.metadataState = 'unknown',
   });
@@ -287,6 +290,9 @@ class _HomePageState extends BaseState<HomePage> {
         fileName: displayName,
         title: hasTitle ? title : null,
         artist: artist.isNotEmpty ? artist : null,
+        artworkPath: (row?['artwork_path'] as String?)?.trim().isNotEmpty == true
+            ? (row!['artwork_path'] as String).trim()
+            : null,
         sourceTag: folderName.isNotEmpty ? '($folderName)' : '',
         metadataState: hasTitle ? 'success' : 'unknown',
       ));
@@ -771,18 +777,19 @@ class _HomePageState extends BaseState<HomePage> {
                                     duration: const Duration(milliseconds: 150),
                                     child: Padding(
                                       padding: const EdgeInsets.symmetric(
-                                          vertical: 6),
+                                          vertical: 2),
                                       child: ListTile(
                                         contentPadding: EdgeInsets.zero,
-                                        leading: const Icon(
-                                          Icons.music_note,
-                                          color: Colors.white38,
-                                          size: 20,
+                                        visualDensity: VisualDensity.compact,
+                                        leading: SongArtwork(
+                                          filePath: song.artworkPath,
+                                          size: 44,
+                                          fallbackIcon: Icons.music_note,
                                         ),
                                         title: Text(
                                           song.displayTitle,
                                           style: const TextStyle(
-                                            fontSize: 17,
+                                            fontSize: 16,
                                             fontWeight: FontWeight.w400,
                                             color: Colors.white,
                                           ),
@@ -792,7 +799,7 @@ class _HomePageState extends BaseState<HomePage> {
                                         subtitle: Text(
                                           song.displaySubtitle,
                                           style: TextStyle(
-                                            fontSize: 14,
+                                            fontSize: 13,
                                             color: Colors.grey[400],
                                           ),
                                           maxLines: 1,

lib/pages/webdav_file_list_page.dart

@@ -351,7 +351,8 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
 
     if (item.isDirectory) {
       return ListTile(
-        contentPadding: const EdgeInsets.symmetric(horizontal: 4, vertical: 2),
+        contentPadding: const EdgeInsets.symmetric(horizontal: 4),
+        visualDensity: VisualDensity.compact,
         leading: const Icon(
           Icons.folder_outlined,
           color: Color(0xFFB8D4D0),
@@ -397,7 +398,8 @@ class _WebDAVFileListPageState extends BaseState<WebDAVFileListPage> {
       ].join(' · ');
 
       return ListTile(
-        contentPadding: const EdgeInsets.symmetric(horizontal: 4, vertical: 2),
+        contentPadding: const EdgeInsets.symmetric(horizontal: 4),
+        visualDensity: VisualDensity.compact,
         leading: SongArtwork(
           filePath: meta?['artwork_path'] as String?,
           size: 44,