refactor(providers): remove dead lookup/history APIs and dedup provider resolution

Delete the verbatim-duplicate LocalLibraryLookup class + provider, the unused
localLibrarySummaryProvider, notifier search()/getCount()/existsInLibrary
wrapper, and the now-orphaned LibraryDatabase.search(); the notifier's async
getById/findExisting lookups (the real ones) stay. Drop dead
download-history removeBySpotifyId/getDatabaseCount and the orphaned
history deleteBySpotifyId, and fold the byte-identical addToHistory/
adoptNativeHistoryItem into one _persistHistoryItem keeping distinct log text.
Delete dead extension_provider members (ensureSpotifyWebExtensionReady,
enabledExtensions, getExtension, resolveProviderDisplayName, URLHandler.matchesURL,
Extension.hasBrowseCategories) and collapse resolveEffectiveDownloadService/
MetadataProvider into one predicate-parameterized helper.

lib/services/history_database.dart

@@ -765,31 +765,6 @@ class HistoryDatabase {
     });
   }
 
-  Future<int> deleteBySpotifyId(String spotifyId) async {
-    final db = await database;
-    final rows = await db.query(
-      'history',
-      columns: ['id'],
-      where: 'spotify_id = ?',
-      whereArgs: [spotifyId],
-    );
-    final ids = rows.map((row) => row['id'] as String).toList(growable: false);
-    return db.transaction<int>((txn) async {
-      for (final id in ids) {
-        await txn.delete(
-          'history_path_keys',
-          where: 'item_id = ?',
-          whereArgs: [id],
-        );
-      }
-      return txn.delete(
-        'history',
-        where: 'spotify_id = ?',
-        whereArgs: [spotifyId],
-      );
-    });
-  }
-
   Future<void> clearAll() async {
     final db = await database;
     await db.transaction((txn) async {

lib/services/library_database.dart

@@ -1862,23 +1862,6 @@ class LibraryDatabase {
     return Sqflite.firstIntValue(result) ?? 0;
   }
 
-  Future<List<Map<String, dynamic>>> search(
-    String query, {
-    int limit = 50,
-  }) async {
-    final db = await database;
-    final searchQuery = '%${_escapeLikePattern(query.toLowerCase())}%';
-    final rows = await db.query(
-      'library',
-      where:
-          "LOWER(track_name) LIKE ? ESCAPE '\\' OR LOWER(artist_name) LIKE ? ESCAPE '\\' OR LOWER(album_name) LIKE ? ESCAPE '\\'",
-      whereArgs: [searchQuery, searchQuery, searchQuery],
-      orderBy: 'track_name',
-      limit: limit,
-    );
-    return rows.map(_dbRowToJson).toList();
-  }
-
   Future<void> close() async {
     final db = await database;
     await db.close();