refactor: remove redundant comments and fix setMetadataSource bug

- Fix setMetadataSource always returning 'deezer' regardless of input parameter
- Remove self-evident doc comments that restate method/class names across
  app_theme, dynamic_color_wrapper, cover_cache_manager, history_database,
  library_database, and download_service_picker
- Remove stale migration inline notes (// 12 -> 16, // 20 -> 16, etc.) from app_theme
- Remove trivial section-label comments in queue_tab batch conversion method
- Remove duplicate 'wait up to 5 seconds' comment in main_shell

lib/services/cover_cache_manager.dart

@@ -37,7 +37,6 @@ class CoverCacheManager {
       final appDir = await getApplicationSupportDirectory();
       _cachePath = p.join(appDir.path, 'cover_cache');
       
-      // Ensure cache directory exists
       await Directory(_cachePath!).create(recursive: true);
       
       debugPrint('CoverCacheManager: Initializing at $_cachePath');
@@ -48,7 +47,6 @@ class CoverCacheManager {
       debugPrint('CoverCacheManager: Initialized successfully');
     } catch (e) {
       debugPrint('CoverCacheManager: Failed to initialize: $e');
-      // Will fallback to DefaultCacheManager
     }
   }
 

lib/services/history_database.dart

@@ -12,7 +12,6 @@ final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
 /// Cached current iOS container path for path normalization
 String? _currentContainerPath;
 
-/// SQLite database service for download history
 /// Provides O(1) lookups by spotify_id and isrc with proper indexing
 class HistoryDatabase {
   static final HistoryDatabase instance = HistoryDatabase._init();
@@ -78,7 +77,6 @@ class HistoryDatabase {
       )
     ''');
 
-    // Indexes for fast lookups
     await db.execute('CREATE INDEX idx_spotify_id ON history(spotify_id)');
     await db.execute('CREATE INDEX idx_isrc ON history(isrc)');
     await db.execute(
@@ -171,7 +169,6 @@ class HistoryDatabase {
     try {
       final db = await database;
 
-      // Get all items with iOS paths
       final rows = await db.query('history', columns: ['id', 'file_path']);
       int updatedCount = 0;
       final batch = db.batch();
@@ -198,7 +195,6 @@ class HistoryDatabase {
         await batch.commit(noResult: true);
       }
 
-      // Save current container path
       await prefs.setString('ios_last_container_path', _currentContainerPath!);
 
       _log.i('iOS path migration complete: $updatedCount paths updated');
@@ -323,7 +319,6 @@ class HistoryDatabase {
     };
   }
 
-  /// Insert or update a history item
   Future<void> upsert(Map<String, dynamic> json) async {
     final db = await database;
     await db.insert(
@@ -345,7 +340,6 @@ class HistoryDatabase {
     return rows.map(_dbRowToJson).toList();
   }
 
-  /// Get item by ID
   Future<Map<String, dynamic>?> getById(String id) async {
     final db = await database;
     final rows = await db.query(
@@ -403,26 +397,22 @@ class HistoryDatabase {
     return rows.map((r) => r['spotify_id'] as String).toSet();
   }
 
-  /// Delete by ID
   Future<void> deleteById(String id) async {
     final db = await database;
     await db.delete('history', where: 'id = ?', whereArgs: [id]);
   }
 
-  /// Delete by Spotify ID
   Future<void> deleteBySpotifyId(String spotifyId) async {
     final db = await database;
     await db.delete('history', where: 'spotify_id = ?', whereArgs: [spotifyId]);
   }
 
-  /// Clear all history
   Future<void> clearAll() async {
     final db = await database;
     await db.delete('history');
     _log.i('Cleared all history');
   }
 
-  /// Get total count
   Future<int> getCount() async {
     final db = await database;
     final result = await db.rawQuery('SELECT COUNT(*) as count FROM history');
@@ -459,7 +449,6 @@ class HistoryDatabase {
     return null;
   }
 
-  /// Close database
   Future<void> close() async {
     final db = await database;
     await db.close();

lib/services/library_database.dart

@@ -123,7 +123,7 @@ class LibraryDatabase {
 
     return await openDatabase(
       path,
-      version: 4, // Bumped version for bitrate column
+      version: 4,
       onConfigure: (db) async {
         await db.rawQuery('PRAGMA journal_mode = WAL');
         await db.execute('PRAGMA synchronous = NORMAL');
@@ -331,13 +331,11 @@ class LibraryDatabase {
     String? trackName,
     String? artistName,
   }) async {
-    // First try ISRC if available
     if (isrc != null && isrc.isNotEmpty) {
       final byIsrc = await getByIsrc(isrc);
       if (byIsrc != null) return byIsrc;
     }
 
-    // Then try name matching
     if (trackName != null && artistName != null) {
       final matches = await findByTrackAndArtist(trackName, artistName);
       if (matches.isNotEmpty) return matches.first;
@@ -523,7 +521,6 @@ class LibraryDatabase {
     return rows.map((r) => r['file_path'] as String).toSet();
   }
 
-  /// Delete multiple items by their file paths
   Future<int> deleteByPaths(List<String> filePaths) async {
     if (filePaths.isEmpty) return 0;
     final db = await database;