feat(mornye): cache motion covers and refine player and search

Save album motion videos in app storage during downloads and prefer offline playback with an aspect-aware layout. Add cache management for saved videos.

Center active lyrics on opening, expand lyrics during manual scrolling, and adjust landscape header spacing. Group search rows and skeletons with dividers and remove redundant result icons.

Validation: Flutter analysis clean; 723 tests passed, 4 skipped; iOS simulator build installed.

lib/screens/settings/cache_management_page.dart

@@ -14,6 +14,8 @@ import 'package:spotiflac_android/providers/download_queue_provider.dart';
 import 'package:spotiflac_android/providers/local_library_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/services/cover_cache_manager.dart';
+import 'package:spotiflac_android/providers/player_motion_artwork_provider.dart';
+import 'package:spotiflac_android/services/motion_artwork_store.dart';
 import 'package:spotiflac_android/services/downloaded_embedded_cover_resolver.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/utils/string_utils.dart';
@@ -72,6 +74,9 @@ class _CacheManagementPageState extends ConsumerState<CacheManagementPage> {
     final tempDirFuture = getTemporaryDirectory();
     final appSupportDirFuture = getApplicationSupportDirectory();
     final coverStatsFuture = CoverCacheManager.getStats();
+    final motionStatsFuture = MotionArtworkStore.defaultDirectory().then(
+      _scanDirectory,
+    );
     final prefsFuture = SharedPreferences.getInstance();
     final trackCacheEntriesFuture = _getTrackCacheSizeSafe();
 
@@ -120,6 +125,7 @@ class _CacheManagementPageState extends ConsumerState<CacheManagementPage> {
       tempStats: tempStats,
       tempIsSameAsAppCache: tempIsSameAsAppCache,
       coverStats: coverStats,
+      motionStats: await motionStatsFuture,
       libraryCoverStats: libraryCoverStats,
       audioAnalysisStats: audioAnalysisStats,
       exploreCacheBytes: exploreBytes,
@@ -205,6 +211,11 @@ class _CacheManagementPageState extends ConsumerState<CacheManagementPage> {
     await CoverCacheManager.clearCache();
   }
 
+  Future<void> _clearMotionArtwork() async {
+    await ref.read(motionArtworkStoreProvider).clear();
+    if (mounted) ref.invalidate(playerMotionArtworkProvider);
+  }
+
   Future<void> _clearLibraryCoverCache() async {
     final appSupportDir = await getApplicationSupportDirectory();
     final libraryCoverDir = Directory('${appSupportDir.path}/library_covers');
@@ -624,6 +635,24 @@ class _CacheManagementPageState extends ConsumerState<CacheManagementPage> {
                       ),
                     ),
                   ),
+                  SettingsItem(
+                    icon: Icons.video_library_outlined,
+                    title: context.l10n.cacheMotionArtwork,
+                    subtitle: _buildSubtitle(
+                      context.l10n.cacheMotionArtworkDesc,
+                      overview.motionStats.totalSizeBytes > 0
+                          ? formatBytes(overview.motionStats.totalSizeBytes)
+                          : context.l10n.cacheNoData,
+                    ),
+                    trailing: _buildClearTrailing(
+                      'clear_motion_artwork',
+                      () => _confirmAndRunAction(
+                        actionKey: 'clear_motion_artwork',
+                        targetLabel: context.l10n.cacheMotionArtwork,
+                        action: _clearMotionArtwork,
+                      ),
+                    ),
+                  ),
                   SettingsItem(
                     icon: Icons.explore_outlined,
                     title: context.l10n.cacheExploreFeed,
@@ -707,6 +736,7 @@ class _CacheOverview {
   final _DirectoryStats? tempStats;
   final bool tempIsSameAsAppCache;
   final CacheStats coverStats;
+  final _DirectoryStats motionStats;
   final _DirectoryStats libraryCoverStats;
   final _DirectoryStats audioAnalysisStats;
   final int exploreCacheBytes;
@@ -720,6 +750,7 @@ class _CacheOverview {
     this.tempStats,
     required this.tempIsSameAsAppCache,
     required this.coverStats,
+    required this.motionStats,
     required this.libraryCoverStats,
     required this.audioAnalysisStats,
     required this.exploreCacheBytes,