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/theme/app_theme.dart

@@ -35,7 +35,6 @@ class AppTheme {
     );
   }
 
-  /// Create dark theme
   static ThemeData dark({
     ColorScheme? dynamicScheme,
     Color? seedColor,
@@ -88,12 +87,11 @@ class AppTheme {
     ),
   );
 
-  /// Card theme
   static CardThemeData _cardTheme(ColorScheme scheme) => CardThemeData(
     elevation: 0,
     shape: RoundedRectangleBorder(
       borderRadius: BorderRadius.circular(16),
-    ), // 12 -> 16
+    ),
     color: scheme.surfaceContainerLow,
     surfaceTintColor: scheme.surfaceTint,
   );
@@ -104,18 +102,17 @@ class AppTheme {
           elevation: 1,
           shape: RoundedRectangleBorder(
             borderRadius: BorderRadius.circular(16),
-          ), // 20 -> 16
+          ),
           padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 12),
         ),
       );
 
-  /// Filled button theme
   static FilledButtonThemeData _filledButtonTheme(ColorScheme scheme) =>
       FilledButtonThemeData(
         style: FilledButton.styleFrom(
           shape: RoundedRectangleBorder(
             borderRadius: BorderRadius.circular(16),
-          ), // 20 -> 16
+          ),
           padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 12),
         ),
       );
@@ -125,18 +122,17 @@ class AppTheme {
         style: OutlinedButton.styleFrom(
           shape: RoundedRectangleBorder(
             borderRadius: BorderRadius.circular(16),
-          ), // 20 -> 16
+          ),
           padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 12),
         ),
       );
 
-  /// Text button theme
   static TextButtonThemeData _textButtonTheme(ColorScheme scheme) =>
       TextButtonThemeData(
         style: TextButton.styleFrom(
           shape: RoundedRectangleBorder(
             borderRadius: BorderRadius.circular(16),
-          ), // 20 -> 16
+          ),
           padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
         ),
       );
@@ -149,40 +145,39 @@ class AppTheme {
         foregroundColor: scheme.onPrimaryContainer,
       );
 
-  /// Input decoration theme
   static InputDecorationTheme _inputDecorationTheme(ColorScheme scheme) =>
       InputDecorationTheme(
         filled: true,
         fillColor: scheme.surfaceContainerHighest.withValues(
           alpha: 0.3,
-        ), // Added transparency
+        ),
         border: OutlineInputBorder(
-          borderRadius: BorderRadius.circular(16), // 12 -> 16
+          borderRadius: BorderRadius.circular(16),
           borderSide: BorderSide.none,
         ),
         enabledBorder: OutlineInputBorder(
-          borderRadius: BorderRadius.circular(16), // 12 -> 16
+          borderRadius: BorderRadius.circular(16),
           borderSide: BorderSide.none,
         ),
         focusedBorder: OutlineInputBorder(
-          borderRadius: BorderRadius.circular(16), // 12 -> 16
+          borderRadius: BorderRadius.circular(16),
           borderSide: BorderSide(color: scheme.primary, width: 2),
         ),
         errorBorder: OutlineInputBorder(
-          borderRadius: BorderRadius.circular(16), // 12 -> 16
+          borderRadius: BorderRadius.circular(16),
           borderSide: BorderSide(color: scheme.error, width: 1),
         ),
         contentPadding: const EdgeInsets.symmetric(
           horizontal: 20,
           vertical: 16,
-        ), // consistent padding
+        ),
       );
 
   static ListTileThemeData _listTileTheme(ColorScheme scheme) =>
       ListTileThemeData(
         shape: RoundedRectangleBorder(
           borderRadius: BorderRadius.circular(16),
-        ), // 12 -> 16
+        ),
         contentPadding: const EdgeInsets.symmetric(horizontal: 16, vertical: 4),
       );
 
@@ -193,7 +188,6 @@ class AppTheme {
     surfaceTintColor: scheme.surfaceTint,
   );
 
-  /// Navigation bar theme
   static NavigationBarThemeData _navigationBarTheme(
     ColorScheme scheme, {
     bool isAmoled = false,
@@ -213,7 +207,6 @@ class AppTheme {
         contentTextStyle: TextStyle(color: scheme.onInverseSurface),
       );
 
-  /// Progress indicator theme
   static ProgressIndicatorThemeData _progressIndicatorTheme(
     ColorScheme scheme,
   ) => ProgressIndicatorThemeData(
@@ -243,7 +236,6 @@ class AppTheme {
     }),
   );
 
-  /// Chip theme
   static ChipThemeData _chipTheme(ColorScheme scheme) => ChipThemeData(
     shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(8)),
     backgroundColor: scheme.surfaceContainerLow,

lib/theme/dynamic_color_wrapper.dart

@@ -4,7 +4,6 @@ import 'package:dynamic_color/dynamic_color.dart';
 import 'package:spotiflac_android/providers/theme_provider.dart';
 import 'package:spotiflac_android/theme/app_theme.dart';
 
-/// Wrapper widget that provides dynamic color support from device wallpaper
 class DynamicColorWrapper extends ConsumerWidget {
   final Widget Function(ThemeData light, ThemeData dark, ThemeMode mode) builder;
 
@@ -23,7 +22,6 @@ class DynamicColorWrapper extends ConsumerWidget {
         ColorScheme darkScheme;
 
         if (themeSettings.useDynamicColor && lightDynamic != null && darkDynamic != null) {
-          // Use dynamic colors from wallpaper (Android 12+)
           lightScheme = lightDynamic;
           darkScheme = darkDynamic;
         } else {
@@ -38,7 +36,6 @@ class DynamicColorWrapper extends ConsumerWidget {
           );
         }
 
-        // Apply AMOLED mode if enabled (pure black background)
         if (themeSettings.useAmoled) {
           darkScheme = _applyAmoledColors(darkScheme);
         }