refactor: extract shared helpers for repeated low-level patterns

Dart:
- notification_service: single _details() builder replaces 13 copies
  of the NotificationDetails block
- platform_bridge: _invokeMap() for 34 invoke+decode call sites,
  _cachedInvoke() unifies the three TTL/in-flight cache scaffolds
- ffmpeg_service: _promoteTempOutput(), _appendCoverInputArgs(),
  single _writeReplayGainTags() and _convertToLossless() for the
  ALAC/FLAC twins
- sqlite_helpers.dart: shared openAppDatabase/path-key/migration
  helpers for the three database classes
- library_collections: parametrized wishlist/loved/favorite CRUD
- extension_provider: one predicate-based replacedBuiltIn* lookup

Go:
- extension runtime: parseGojaHeaders/coerceGojaBody/doExtensionHTTP
  shared by httpGet/httpPost/httpRequest/shortcuts/fetch
- exports_metadata: applyAudioMetadataToResult + successMethodJSON,
  APE edit path reuses audioMetadataFromEditFields
- lyrics: lrclibGet() for both LRCLib fetchers
- extension_store: drop hand-rolled strings helpers

lib/services/sqlite_helpers.dart

@@ -0,0 +1,102 @@
+import 'package:path/path.dart';
+import 'package:path_provider/path_provider.dart';
+import 'package:spotiflac_android/utils/logger.dart';
+import 'package:spotiflac_android/utils/path_match_keys.dart';
+import 'package:sqflite/sqflite.dart';
+
+final _log = AppLogger('AppSqlite');
+
+/// Opens a database file in the app documents directory with the shared
+/// WAL + synchronous=NORMAL configuration.
+Future<Database> openAppDatabase(
+  String fileName, {
+  required int version,
+  required Future<void> Function(Database db, int version) onCreate,
+  required Future<void> Function(Database db, int oldVersion, int newVersion)
+  onUpgrade,
+  bool foreignKeys = false,
+}) async {
+  final dbPath = await getApplicationDocumentsDirectory();
+  final path = join(dbPath.path, fileName);
+
+  _log.i('Initializing database at: $path');
+
+  return openDatabase(
+    path,
+    version: version,
+    onConfigure: (db) async {
+      if (foreignKeys) {
+        await db.execute('PRAGMA foreign_keys = ON');
+      }
+      await db.rawQuery('PRAGMA journal_mode = WAL');
+      await db.execute('PRAGMA synchronous = NORMAL');
+    },
+    onCreate: onCreate,
+    onUpgrade: onUpgrade,
+  );
+}
+
+String normalizeLookupText(String? value) {
+  return (value ?? '').trim().toLowerCase();
+}
+
+Future<void> addColumnIfMissing(
+  Database db,
+  String table,
+  String column,
+  String type,
+) async {
+  final columns = await db.rawQuery('PRAGMA table_info($table)');
+  final exists = columns.any(
+    (row) => (row['name']?.toString().toLowerCase() ?? '') == column,
+  );
+  if (!exists) {
+    await db.execute('ALTER TABLE $table ADD COLUMN $column $type');
+  }
+}
+
+Future<void> createPathKeyTable(DatabaseExecutor db, String table) async {
+  await db.execute('''
+    CREATE TABLE IF NOT EXISTS $table (
+      item_id TEXT NOT NULL,
+      path_key TEXT NOT NULL,
+      PRIMARY KEY (item_id, path_key)
+    )
+  ''');
+  await db.execute(
+    'CREATE INDEX IF NOT EXISTS idx_${table}_key ON $table(path_key)',
+  );
+}
+
+Future<void> backfillPathKeys(
+  Database db,
+  String sourceTable,
+  String keyTable,
+) async {
+  final rows = await db.query(sourceTable, columns: ['id', 'file_path']);
+  final batch = db.batch();
+  for (final row in rows) {
+    putPathKeysInBatch(
+      batch,
+      keyTable,
+      row['id'] as String,
+      row['file_path'] as String?,
+    );
+  }
+  await batch.commit(noResult: true);
+}
+
+void putPathKeysInBatch(
+  Batch batch,
+  String table,
+  String id,
+  String? filePath,
+) {
+  batch.delete(table, where: 'item_id = ?', whereArgs: [id]);
+  for (final key in buildPathMatchKeys(filePath)) {
+    batch.insert(table, {
+      'item_id': id,
+      'path_key': key,
+    }, conflictAlgorithm: ConflictAlgorithm.ignore);
+  }
+}