feat: add resolve API with SongLink fallback, fix multi-artist tags (#288), and cleanup

Resolve API (api.zarz.moe):
- Refactor songlink.go: Spotify URLs use resolve API, non-Spotify uses SongLink API
- Add SongLink fallback when resolve API fails for Spotify (two-layer resilience)
- Remove dead code: page parser, XOR-obfuscated keys, legacy helpers

Multi-artist tag fix (#288):
- Add RewriteSplitArtistTags() in Go to rewrite ARTIST/ALBUMARTIST as split Vorbis comments
- Wire method channel handler in Android (MainActivity.kt) and iOS (AppDelegate.swift)
- Add PlatformBridge.rewriteSplitArtistTags() in Dart
- Call native FLAC rewriter after FFmpeg embed when split_vorbis mode is active
- Extract deezerTrackArtistDisplay() helper to use Contributors in album/playlist tracks

Code cleanup:
- Remove unused imports, dead code, and redundant comments across Go and Dart
- Fix build: remove stale getQobuzDebugKey() reference in deezer_download.go

lib/widgets/animation_utils.dart

@@ -1,9 +1,5 @@
 import 'package:flutter/material.dart';
 
-// ─────────────────────────────────────────────────────────────────────────────
-// 1. Staggered List Item – fade + slide-up entrance with index-based delay
-// ─────────────────────────────────────────────────────────────────────────────
-
 /// Wraps a child in a staggered fade-in + slide-up animation.
 ///
 /// [index] controls the stagger delay (each item delayed by [staggerDelay]).
@@ -31,7 +27,6 @@ class StaggeredListItem extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     if (!animate || index >= maxAnimatedItems) return child;
-    // Cap the delay so very long lists don't have absurd wait times.
     final cappedIndex = index.clamp(0, maxAnimatedItems - 1);
     final delay = staggerDelay * cappedIndex;
     final totalDuration = duration + delay;
@@ -42,7 +37,6 @@ class StaggeredListItem extends StatelessWidget {
       duration: totalDuration,
       curve: Curves.easeOutCubic,
       builder: (context, value, child) {
-        // Compute the effective progress after the stagger delay.
         final delayFraction = totalDuration.inMilliseconds > 0
             ? delay.inMilliseconds / totalDuration.inMilliseconds
             : 0.0;
@@ -62,10 +56,6 @@ class StaggeredListItem extends StatelessWidget {
   }
 }
 
-// ─────────────────────────────────────────────────────────────────────────────
-// 2. Animated State Switcher – crossfade between loading / content / empty / error
-// ─────────────────────────────────────────────────────────────────────────────
-
 /// A convenience wrapper around [AnimatedSwitcher] that crossfades between
 /// different widget states (loading, content, empty, error).
 ///
@@ -94,10 +84,6 @@ class AnimatedStateSwitcher extends StatelessWidget {
   }
 }
 
-// ─────────────────────────────────────────────────────────────────────────────
-// 3. Shared Page Route – consistent slide-from-right transition
-// ─────────────────────────────────────────────────────────────────────────────
-
 /// Creates a platform-aware material route.
 ///
 /// This intentionally defers route transitions to Flutter's material route and
@@ -107,10 +93,6 @@ Route<T> slidePageRoute<T>({required Widget page}) {
   return MaterialPageRoute<T>(builder: (context) => page);
 }
 
-// ─────────────────────────────────────────────────────────────────────────────
-// 4. Shimmer / Skeleton Loading Widget
-// ─────────────────────────────────────────────────────────────────────────────
-
 /// A shimmer effect widget that can wrap skeleton placeholders.
 class ShimmerLoading extends StatefulWidget {
   final Widget child;
@@ -682,10 +664,6 @@ class HomeSearchSkeleton extends StatelessWidget {
   }
 }
 
-// ─────────────────────────────────────────────────────────────────────────────
-// 5. Animated Selection Checkbox – scales in when entering selection mode
-// ─────────────────────────────────────────────────────────────────────────────
-
 /// An animated selection indicator that scales in/out and crossfades the
 /// checked/unchecked state.
 class AnimatedSelectionCheckbox extends StatelessWidget {
@@ -746,10 +724,6 @@ class AnimatedSelectionCheckbox extends StatelessWidget {
   }
 }
 
-// ─────────────────────────────────────────────────────────────────────────────
-// 6. Download Success Animation – green flash + checkmark
-// ─────────────────────────────────────────────────────────────────────────────
-
 /// A widget that briefly flashes a success color behind its child and shows
 /// an animated checkmark when [showSuccess] transitions to true.
 class DownloadSuccessOverlay extends StatefulWidget {
@@ -775,8 +749,6 @@ class _DownloadSuccessOverlayState extends State<DownloadSuccessOverlay>
   @override
   void initState() {
     super.initState();
-    // Initialise from the current widget value so items that are already
-    // completed when first built do not play the flash animation.
     _wasSuccess = widget.showSuccess;
     _controller = AnimationController(
       vsync: this,
@@ -821,10 +793,6 @@ class _DownloadSuccessOverlayState extends State<DownloadSuccessOverlay>
   }
 }
 
-// ─────────────────────────────────────────────────────────────────────────────
-// 7. Badge Bump Animation – scales the badge when count changes
-// ─────────────────────────────────────────────────────────────────────────────
-
 /// Wraps a [Badge] child and plays a brief scale-bump whenever [count] changes.
 class AnimatedBadge extends StatefulWidget {
   final int count;
@@ -877,10 +845,6 @@ class _AnimatedBadgeState extends State<AnimatedBadge>
   }
 }
 
-// ─────────────────────────────────────────────────────────────────────────────
-// 8. Animated Removal Item – fade + slide out when removed from a list
-// ─────────────────────────────────────────────────────────────────────────────
-
 /// Build a removal animation for [AnimatedList] items.
 /// Use as the `builder` callback in [AnimatedListState.removeItem].
 Widget buildRemovalAnimation(Widget child, Animation<double> animation) {

lib/widgets/batch_progress_dialog.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
 
-/// Progress state communicated from caller to dialog via [ValueNotifier].
 class _BatchProgress {
   final int current;
   final String? detail;
@@ -54,11 +53,8 @@ class BatchProgressDialog extends StatefulWidget {
     required ValueNotifier<_BatchProgress> progressNotifier,
   }) : _progressNotifier = progressNotifier;
 
-  // ── Static bookkeeping ──────────────────────────────────────────────
-
   static ValueNotifier<_BatchProgress>? _activeNotifier;
 
-  /// Show the dialog. Call [update] to push progress, [dismiss] to close.
   static void show({
     required BuildContext context,
     required String title,
@@ -82,13 +78,10 @@ class BatchProgressDialog extends StatefulWidget {
     );
   }
 
-  /// Update the progress of the currently visible dialog.
-  /// No [BuildContext] needed – communicates via [ValueNotifier].
   static void update({required int current, String? detail}) {
     _activeNotifier?.value = _BatchProgress(current: current, detail: detail);
   }
 
-  /// Dismiss the dialog and clean up.
   static void dismiss(BuildContext context) {
     _activeNotifier = null;
     Navigator.of(context, rootNavigator: true).pop();

lib/widgets/collapsing_header.dart

@@ -1,8 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:spotiflac_android/utils/app_bar_layout.dart';
 
-/// A collapsing header widget
-/// Title collapses from large to small when scrolling
 class CollapsingHeader extends StatelessWidget {
   final String title;
   final bool showBackButton;
@@ -100,7 +98,6 @@ class CollapsingHeader extends StatelessWidget {
   }
 }
 
-/// Section header for settings
 class SettingsSection extends StatelessWidget {
   final String title;
   const SettingsSection({super.key, required this.title});
@@ -120,7 +117,6 @@ class SettingsSection extends StatelessWidget {
   }
 }
 
-/// Info card widget (like version info)
 class InfoCard extends StatelessWidget {
   final IconData icon;
   final String title;

lib/widgets/donate_icons.dart

@@ -1,7 +1,5 @@
 import 'package:flutter/material.dart';
 
-/// Custom painted icons for donate platforms
-
 class KofiIcon extends StatelessWidget {
   final double size;
   final Color color;
@@ -46,7 +44,6 @@ class _KofiPainter extends CustomPainter {
       ..quadraticBezierTo(s * 0.92, s * 0.68, s * 0.70, s * 0.68);
     canvas.drawPath(handlePath, handlePaint);
 
-    // Heart on cup
     final heartPaint = Paint()
       ..color = const Color(0xFFFF5E5B)
       ..style = PaintingStyle.fill;
@@ -62,7 +59,6 @@ class _KofiPainter extends CustomPainter {
       ..close();
     canvas.drawPath(heart, heartPaint);
 
-    // Steam lines
     final steamPaint = Paint()
       ..color = color.withValues(alpha: 0.6)
       ..style = PaintingStyle.stroke
@@ -108,12 +104,9 @@ class _GitHubPainter extends CustomPainter {
       ..color = color
       ..style = PaintingStyle.fill;
 
-    // GitHub octocat silhouette (simplified mark)
-    // Based on the GitHub logo path, scaled to fit
     final scale = s / 24.0;
 
     final path = Path();
-    // Outer circle/head shape
     path.moveTo(12 * scale, 0.5 * scale);
     path.cubicTo(
       5.37 * scale, 0.5 * scale,
@@ -135,7 +128,6 @@ class _GitHubPainter extends CustomPainter {
       9.01 * scale, 22.01 * scale,
       9.01 * scale, 21.01 * scale,
     );
-    // Left arm
     path.cubicTo(
       5.67 * scale, 21.71 * scale,
       4.97 * scale, 19.56 * scale,

lib/widgets/download_service_picker.dart

@@ -5,7 +5,6 @@ import 'package:spotiflac_android/providers/extension_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
 
-/// Built-in service info with quality options
 class BuiltInService {
   final String id;
   final String label;
@@ -22,7 +21,6 @@ class BuiltInService {
   });
 }
 
-/// Default quality options for each built-in service
 const _builtInServices = [
   BuiltInService(
     id: 'tidal',
@@ -99,7 +97,6 @@ class DownloadServicePicker extends ConsumerStatefulWidget {
   ConsumerState<DownloadServicePicker> createState() =>
       _DownloadServicePickerState();
 
-  /// Show the download service picker as a modal bottom sheet
   static void show(
     BuildContext context, {
     String? trackName,
@@ -135,7 +132,6 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
   @override
   void initState() {
     super.initState();
-    // Default to recommended service if available, otherwise use default
     final recommended = widget.recommendedService;
     if (recommended != null && recommended.isNotEmpty) {
       _selectedService = recommended;
@@ -144,7 +140,6 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
     }
   }
 
-  /// Get quality options for the selected service
   List<QualityOption> _getQualityOptions() {
     final builtIn = _builtInServices
         .where((s) => s.id == _selectedService)
@@ -161,8 +156,6 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
       return ext.qualityOptions;
     }
 
-    // Extensions without quality options use Tidal's options as default
-    // since the download will fall back to built-in providers anyway.
     return _builtInServices.firstWhere((s) => s.id == 'tidal').qualityOptions;
   }
 

lib/widgets/re_enrich_field_dialog.dart

@@ -29,10 +29,6 @@ class ReEnrichFieldSelection {
   bool get isAll => fields.length == ReEnrichFields.all.length;
 }
 
-/// Shows a bottom sheet that lets the user pick which metadata fields to update
-/// during a bulk re-enrich operation.
-///
-/// Returns `null` when cancelled, or a [ReEnrichFieldSelection] when confirmed.
 Future<ReEnrichFieldSelection?> showReEnrichFieldDialog(
   BuildContext context, {
   required int selectedCount,
@@ -128,7 +124,6 @@ class _ReEnrichFieldSheetState extends State<_ReEnrichFieldSheet> {
         mainAxisSize: MainAxisSize.min,
         crossAxisAlignment: CrossAxisAlignment.start,
         children: [
-          // Title
           Padding(
             padding: const EdgeInsets.fromLTRB(24, 0, 24, 4),
             child: Text(
@@ -138,7 +133,6 @@ class _ReEnrichFieldSheetState extends State<_ReEnrichFieldSheet> {
               ),
             ),
           ),
-          // Subtitle
           Padding(
             padding: const EdgeInsets.fromLTRB(24, 0, 24, 4),
             child: Text(
@@ -158,7 +152,6 @@ class _ReEnrichFieldSheetState extends State<_ReEnrichFieldSheet> {
             ),
           ),
           const Divider(height: 1),
-          // Select All
           CheckboxListTile(
             contentPadding: const EdgeInsets.symmetric(horizontal: 16),
             title: Text(
@@ -171,7 +164,6 @@ class _ReEnrichFieldSheetState extends State<_ReEnrichFieldSheet> {
             controlAffinity: ListTileControlAffinity.leading,
           ),
           const Divider(height: 1, indent: 16, endIndent: 16),
-          // Individual fields
           for (final field in ReEnrichFields.all)
             CheckboxListTile(
               contentPadding: const EdgeInsets.symmetric(horizontal: 16),
@@ -182,7 +174,6 @@ class _ReEnrichFieldSheetState extends State<_ReEnrichFieldSheet> {
               controlAffinity: ListTileControlAffinity.leading,
             ),
           const SizedBox(height: 8),
-          // Confirm button
           Padding(
             padding: const EdgeInsets.fromLTRB(16, 8, 16, 16),
             child: SizedBox(

lib/widgets/settings_group.dart

@@ -1,7 +1,5 @@
 import 'package:flutter/material.dart';
 
-/// A grouped settings card that connects items together like Android Settings
-/// Items are connected with no gap between them, only separated when changing groups
 class SettingsGroup extends StatelessWidget {
   final List<Widget> children;
   final EdgeInsetsGeometry? margin;
@@ -17,14 +15,10 @@ class SettingsGroup extends StatelessWidget {
     final colorScheme = Theme.of(context).colorScheme;
     final isDark = Theme.of(context).brightness == Brightness.dark;
     
-    // Use a more contrasting color for cards
-    // In dark mode with dynamic color, surfaceContainerHighest can be too similar to surface
-    // So we add a slight white overlay to make it more visible
-    // In light mode with dynamic color, we add a slight black overlay for the same reason
     final cardColor = isDark 
         ? Color.alphaBlend(Colors.white.withValues(alpha: 0.08), colorScheme.surface)
         : Color.alphaBlend(Colors.black.withValues(alpha: 0.04), colorScheme.surface);
-    
+
     return Container(
       margin: margin ?? const EdgeInsets.symmetric(horizontal: 16, vertical: 4),
       decoration: BoxDecoration(
@@ -44,7 +38,6 @@ class SettingsGroup extends StatelessWidget {
 }
 
 class SettingsItem extends StatelessWidget {
-
   final IconData? icon;
   final String title;
   final String? subtitle;
@@ -126,7 +119,6 @@ class SettingsItem extends StatelessWidget {
 }
 
 class SettingsSwitchItem extends StatelessWidget {
-
   final IconData? icon;
   final String title;
   final String? subtitle;
@@ -214,7 +206,6 @@ class SettingsSwitchItem extends StatelessWidget {
 }
 
 class SettingsSectionHeader extends StatelessWidget {
-
   final String title;
 
   const SettingsSectionHeader({super.key, required this.title});

lib/widgets/track_collection_quick_actions.dart

@@ -74,7 +74,6 @@ class _TrackOptionsSheet extends ConsumerWidget {
           child: Column(
             mainAxisSize: MainAxisSize.min,
             children: [
-              // Header with drag handle + track info (matches _TrackInfoHeader)
               Column(
                 children: [
                   const SizedBox(height: 8),
@@ -163,7 +162,6 @@ class _TrackOptionsSheet extends ConsumerWidget {
                 color: colorScheme.outlineVariant.withValues(alpha: 0.5),
               ),
 
-              // Action items (matches _QualityOption style)
               _OptionTile(
                 icon: isLoved ? Icons.favorite : Icons.favorite_border,
                 iconColor: isLoved ? colorScheme.error : null,
@@ -234,7 +232,6 @@ class _TrackOptionsSheet extends ConsumerWidget {
   }
 }
 
-/// Styled like _QualityOption in download_service_picker.dart
 class _OptionTile extends StatelessWidget {
   final IconData icon;
   final Color? iconColor;