feat: compact media library sqlite storage

lib/core/storage/media_library_store.dart

@@ -22,7 +22,7 @@ class MediaLibraryStore {
     );
     _database = await openDatabase(
       databasePath,
-      version: 2,
+      version: 3,
       onCreate: (db, _) async {
         await _createSchema(db);
       },
@@ -198,7 +198,7 @@ class MediaLibraryStore {
     });
   }
 
-  Future<void> importBackup(String backupPath) async {
+  Future<MediaLibraryStorageStats> importBackup(String backupPath) async {
     final db = await _db;
     await db.execute('ATTACH DATABASE ? AS imported_backup', [backupPath]);
     try {
@@ -216,6 +216,26 @@ class MediaLibraryStore {
     } finally {
       await db.execute('DETACH DATABASE imported_backup');
     }
+    return optimizeStorage();
+  }
+
+  /// Reclaims space used by imported backdrop BLOBs. Posters remain available
+  /// for offline poster walls; backdrops can always be fetched from TMDB again.
+  Future<MediaLibraryStorageStats> optimizeStorage() async {
+    final db = await _db;
+    final before = await _databaseBytes(db.path);
+    final removedBackdrops = await db.rawUpdate(
+      'UPDATE media_items SET backdrop = NULL WHERE backdrop IS NOT NULL',
+    );
+    await db.execute('PRAGMA wal_checkpoint(TRUNCATE)');
+    await db.execute('PRAGMA optimize');
+    await db.execute('VACUUM');
+    final after = await _databaseBytes(db.path);
+    return MediaLibraryStorageStats(
+      beforeBytes: before,
+      afterBytes: after,
+      removedBackdropCount: removedBackdrops,
+    );
   }
 
   Future<void> exportBackupTo(String destinationPath) async {
@@ -477,6 +497,17 @@ class MediaLibraryStore {
         children_json TEXT NOT NULL
       )
     ''');
+    await db.execute(
+      'CREATE INDEX IF NOT EXISTS idx_media_items_library_title '
+      'ON media_items(library_id, title COLLATE NOCASE)',
+    );
+    await db.execute(
+      'CREATE INDEX IF NOT EXISTS idx_media_items_tmdb_id '
+      'ON media_items(tmdb_id)',
+    );
+    await db.execute(
+      'CREATE INDEX IF NOT EXISTS idx_file_index_gcid ON file_index(gcid)',
+    );
   }
 
   MediaLibraryItem _itemFromRow(Map<String, Object?> row) {
@@ -571,4 +602,27 @@ class MediaLibraryStore {
     'updated_at',
   ];
   static String _folderID(String? folderID) => folderID ?? _rootFolderID;
+
+  Future<int> _databaseBytes(String databasePath) async {
+    var bytes = 0;
+    for (final suffix in const ['', '-wal', '-shm']) {
+      final file = File('$databasePath$suffix');
+      if (await file.exists()) bytes += await file.length();
+    }
+    return bytes;
+  }
+}
+
+class MediaLibraryStorageStats {
+  final int beforeBytes;
+  final int afterBytes;
+  final int removedBackdropCount;
+
+  const MediaLibraryStorageStats({
+    required this.beforeBytes,
+    required this.afterBytes,
+    required this.removedBackdropCount,
+  });
+
+  int get reclaimedBytes => (beforeBytes - afterBytes).clamp(0, beforeBytes);
 }

lib/pages/media_library_page.dart

@@ -249,6 +249,14 @@ class _MediaLibraryPageState extends ConsumerState<MediaLibraryPage> {
           child: const Text('导入数据'),
         ),
         const SizedBox(width: 8),
+        ShadButton.outline(
+          onPressed: _backupBusy || state.isScanning
+              ? null
+              : _optimizeScrapedStorage,
+          leading: const Icon(Icons.cleaning_services_rounded, size: 16),
+          child: const Text('数据库瘦身'),
+        ),
+        const SizedBox(width: 8),
         ShadButton.outline(
           onPressed: state.selectedLibrary == null || state.isScanning
               ? null
@@ -785,6 +793,15 @@ class _MediaLibraryPageState extends ConsumerState<MediaLibraryPage> {
     }
   }
 
+  Future<void> _optimizeScrapedStorage() async {
+    setState(() => _backupBusy = true);
+    try {
+      await ref.read(mediaLibraryProvider.notifier).optimizeLocalStorage();
+    } finally {
+      if (mounted) setState(() => _backupBusy = false);
+    }
+  }
+
   Future<void> _searchTMDB(String query) async {
     final text = query.trim();
     if (text.isEmpty || _tmdbApiKey.isEmpty) return;

lib/providers/media_library_provider.dart

@@ -207,7 +207,7 @@ class MediaLibraryNotifier extends StateNotifier<MediaLibraryState> {
       clearStatus: true,
     );
     try {
-      await _store.importBackup(backupPath);
+      final stats = await _store.importBackup(backupPath);
       final libraries = await _loadLibraries();
       final selectedID = libraries.isEmpty ? null : libraries.first.id;
       state = state.copyWith(
@@ -215,7 +215,7 @@ class MediaLibraryNotifier extends StateNotifier<MediaLibraryState> {
         selectedLibraryID: selectedID,
         clearSelectedLibrary: selectedID == null,
         items: selectedID == null ? const [] : await _loadItems(selectedID),
-        statusMessage: '刮削数据已导入',
+        statusMessage: '刮削数据已导入，已回收 ${_formatBytes(stats.reclaimedBytes)}',
       );
     } catch (error) {
       state = state.copyWith(errorMessage: '导入失败：$error');
@@ -241,6 +241,27 @@ class MediaLibraryNotifier extends StateNotifier<MediaLibraryState> {
     }
   }
 
+  Future<void> optimizeLocalStorage() async {
+    if (state.isLoading || state.isScanning) return;
+    state = state.copyWith(
+      isLoading: true,
+      clearError: true,
+      clearStatus: true,
+    );
+    try {
+      final stats = await _store.optimizeStorage();
+      state = state.copyWith(
+        statusMessage: stats.removedBackdropCount == 0
+            ? '本地刮削数据库已是最优状态'
+            : '已清理 ${stats.removedBackdropCount} 张背景图，回收 ${_formatBytes(stats.reclaimedBytes)}',
+      );
+    } catch (error) {
+      state = state.copyWith(errorMessage: '数据库优化失败：$error');
+    } finally {
+      state = state.copyWith(isLoading: false);
+    }
+  }
+
   Future<void> scanSelectedLibrary() async {
     final library = state.selectedLibrary;
     if (library == null || _api == null || state.isScanning) return;
@@ -485,6 +506,15 @@ class MediaLibraryNotifier extends StateNotifier<MediaLibraryState> {
     return int.tryParse(value?.toString() ?? '');
   }
 
+  String _formatBytes(int bytes) {
+    if (bytes < 1024) return '$bytes B';
+    if (bytes < 1024 * 1024) return '${(bytes / 1024).toStringAsFixed(1)} KB';
+    if (bytes < 1024 * 1024 * 1024) {
+      return '${(bytes / (1024 * 1024)).toStringAsFixed(1)} MB';
+    }
+    return '${(bytes / (1024 * 1024 * 1024)).toStringAsFixed(1)} GB';
+  }
+
   Future<void> _scanSource(
     String? rootID,
     String rootPath, {