perf: lazy extension VM init, incremental startup maintenance, and UI optimizations

- Defer extension VM initialization until first use with lockReadyVM() pattern to eliminate TOCTOU races and reduce startup overhead
- Add validateExtensionLoad() to catch JS errors at install time without keeping VM alive
- Teardown VM on extension disable to free resources; re-init lazily on re-enable
- Replace full orphan cleanup with incremental cursor-based pagination across launches
- Batch DB writes (upsertBatch, replaceAll) with transactions for atomicity
- Parse JSON natively on Kotlin side to avoid double-serialization over MethodChannel
- Add identity-based memoization caches for unified items and path match keys in queue tab
- Use ValueListenableBuilder for targeted embedded cover refreshes instead of full setState
- Extract shared widgets (_buildAlbumGridItemCore, _buildFilterButton, _navigateWithUnfocus)
- Use libraryCollectionsProvider selector and MediaQuery.paddingOf for fewer rebuilds
- Simplify supporter chip tiers and localize remaining hardcoded strings

lib/services/history_database.dart

@@ -328,6 +328,20 @@ class HistoryDatabase {
     );
   }
 
+  Future<void> upsertBatch(List<Map<String, dynamic>> items) async {
+    if (items.isEmpty) return;
+    final db = await database;
+    final batch = db.batch();
+    for (final json in items) {
+      batch.insert(
+        'history',
+        _jsonToDbRow(json),
+        conflictAlgorithm: ConflictAlgorithm.replace,
+      );
+    }
+    await batch.commit(noResult: true);
+  }
+
   /// Get all history items ordered by download date (newest first)
   Future<List<Map<String, dynamic>>> getAll({int? limit, int? offset}) async {
     final db = await database;
@@ -532,6 +546,29 @@ class HistoryDatabase {
     return rows.map((r) => Map<String, dynamic>.from(r)).toList();
   }
 
+  Future<List<Map<String, dynamic>>> getEntriesWithPathsPage({
+    required int limit,
+    int offset = 0,
+  }) async {
+    final db = await database;
+    final rows = await db.query(
+      'history',
+      columns: [
+        'id',
+        'file_path',
+        'storage_mode',
+        'download_tree_uri',
+        'saf_relative_dir',
+        'saf_file_name',
+      ],
+      where: 'file_path IS NOT NULL AND file_path != ""',
+      orderBy: 'downloaded_at DESC, id DESC',
+      limit: limit,
+      offset: offset,
+    );
+    return rows.map((r) => Map<String, dynamic>.from(r)).toList();
+  }
+
   /// Delete multiple entries by IDs
   Future<int> deleteByIds(List<String> ids) async {
     if (ids.isEmpty) return 0;

lib/services/library_database.dart

@@ -255,20 +255,41 @@ class LibraryDatabase {
   Future<void> upsertBatch(List<Map<String, dynamic>> items) async {
     if (items.isEmpty) return;
     final db = await database;
-    final batch = db.batch();
-
-    for (final json in items) {
-      batch.insert(
-        'library',
-        _jsonToDbRow(json),
-        conflictAlgorithm: ConflictAlgorithm.replace,
-      );
-    }
-
-    await batch.commit(noResult: true);
+    await db.transaction((txn) async {
+      final batch = txn.batch();
+      for (final json in items) {
+        batch.insert(
+          'library',
+          _jsonToDbRow(json),
+          conflictAlgorithm: ConflictAlgorithm.replace,
+        );
+      }
+      await batch.commit(noResult: true);
+    });
     _log.i('Batch inserted ${items.length} items');
   }
 
+  Future<void> replaceAll(List<Map<String, dynamic>> items) async {
+    final db = await database;
+    await db.transaction((txn) async {
+      await txn.delete('library');
+      if (items.isEmpty) {
+        return;
+      }
+
+      final batch = txn.batch();
+      for (final json in items) {
+        batch.insert(
+          'library',
+          _jsonToDbRow(json),
+          conflictAlgorithm: ConflictAlgorithm.replace,
+        );
+      }
+      await batch.commit(noResult: true);
+    });
+    _log.i('Replaced library with ${items.length} items');
+  }
+
   Future<List<Map<String, dynamic>>> getAll({int? limit, int? offset}) async {
     final db = await database;
     final rows = await db.query(

lib/services/platform_bridge.dart

@@ -83,24 +83,18 @@ class PlatformBridge {
 
   static Future<Map<String, dynamic>> getDownloadProgress() async {
     final result = await _channel.invokeMethod('getDownloadProgress');
-    return jsonDecode(result as String) as Map<String, dynamic>;
+    return _decodeMapResult(result);
   }
 
   static Future<Map<String, dynamic>> getAllDownloadProgress() async {
     final result = await _channel.invokeMethod('getAllDownloadProgress');
-    return jsonDecode(result as String) as Map<String, dynamic>;
+    return _decodeMapResult(result);
   }
 
   static Stream<Map<String, dynamic>> downloadProgressStream() {
-    return _downloadProgressEvents.receiveBroadcastStream().map((event) {
-      if (event is String) {
-        return jsonDecode(event) as Map<String, dynamic>;
-      }
-      if (event is Map) {
-        return Map<String, dynamic>.from(event);
-      }
-      return const <String, dynamic>{};
-    });
+    return _downloadProgressEvents
+        .receiveBroadcastStream()
+        .map(_decodeMapResult);
   }
 
   static Future<void> exitApp() async {
@@ -1186,19 +1180,13 @@ class PlatformBridge {
   /// Get current library scan progress
   static Future<Map<String, dynamic>> getLibraryScanProgress() async {
     final result = await _channel.invokeMethod('getLibraryScanProgress');
-    return jsonDecode(result as String) as Map<String, dynamic>;
+    return _decodeMapResult(result);
   }
 
   static Stream<Map<String, dynamic>> libraryScanProgressStream() {
-    return _libraryScanProgressEvents.receiveBroadcastStream().map((event) {
-      if (event is String) {
-        return jsonDecode(event) as Map<String, dynamic>;
-      }
-      if (event is Map) {
-        return Map<String, dynamic>.from(event);
-      }
-      return const <String, dynamic>{};
-    });
+    return _libraryScanProgressEvents
+        .receiveBroadcastStream()
+        .map(_decodeMapResult);
   }
 
   /// Cancel ongoing library scan
@@ -1206,6 +1194,20 @@ class PlatformBridge {
     await _channel.invokeMethod('cancelLibraryScan');
   }
 
+  static Map<String, dynamic> _decodeMapResult(dynamic result) {
+    if (result is Map) {
+      return Map<String, dynamic>.from(result);
+    }
+    if (result is String) {
+      if (result.isEmpty) return const <String, dynamic>{};
+      final decoded = jsonDecode(result);
+      if (decoded is Map) {
+        return Map<String, dynamic>.from(decoded);
+      }
+    }
+    return const <String, dynamic>{};
+  }
+
   // MARK: - iOS Security-Scoped Bookmark
 
   /// Create a security-scoped bookmark from a filesystem path picked by