feat(metadata): remove ReplayGain from individual and selected tracks

lib/services/batch_track_actions.dart

@@ -536,7 +536,7 @@ Future<void> _performBatchConversion(
   }
 }
 
-/// Batch-scans loudness and writes ReplayGain tags to [selectedItems].
+/// Adds or removes ReplayGain tags for [selectedItems].
 ///
 /// [onConfirmOpen] / [onConfirmClosed] let the caller hide and restore any
 /// selection UI around the confirmation dialog; [onConfirmClosed] receives
@@ -545,6 +545,7 @@ Future<void> runBatchReplayGain(
   BuildContext context,
   List<UnifiedLibraryItem> selectedItems, {
   required VoidCallback onExitSelectionMode,
+  bool remove = false,
   VoidCallback? onConfirmOpen,
   Future<void> Function(bool confirmed)? onConfirmClosed,
 }) async {
@@ -555,9 +556,15 @@ Future<void> runBatchReplayGain(
   final confirmed = await showAppDialog<bool>(
     context: context,
     builder: (ctx) => AppAlertDialog(
-      title: Text(ctx.l10n.replayGainBatchConfirmTitle),
+      title: Text(
+        remove
+            ? ctx.l10n.trackRemoveReplayGain
+            : ctx.l10n.replayGainBatchConfirmTitle,
+      ),
       content: Text(
-        ctx.l10n.replayGainBatchConfirmMessage(selectedItems.length),
+        remove
+            ? ctx.l10n.replayGainRemoveConfirmMessage(selectedItems.length)
+            : ctx.l10n.replayGainBatchConfirmMessage(selectedItems.length),
       ),
       actions: [
         AppDialogAction(
@@ -568,7 +575,11 @@ Future<void> runBatchReplayGain(
           filled: true,
           isDefault: true,
           onPressed: () => Navigator.pop(ctx, true),
-          child: Text(ctx.l10n.replayGainBatchConfirmTitle),
+          child: Text(
+            remove
+                ? ctx.l10n.trackRemoveReplayGain
+                : ctx.l10n.replayGainBatchConfirmTitle,
+          ),
         ),
       ],
     ),
@@ -585,7 +596,9 @@ Future<void> runBatchReplayGain(
 
   BatchProgressDialog.show(
     context: context,
-    title: context.l10n.replayGainBatchAnalyzing,
+    title: remove
+        ? context.l10n.replayGainRemoving
+        : context.l10n.replayGainBatchAnalyzing,
     total: total,
     icon: Icons.graphic_eq,
     onCancel: () {
@@ -599,10 +612,12 @@ Future<void> runBatchReplayGain(
     final item = selectedItems[i];
     BatchProgressDialog.update(current: i + 1, detail: item.trackName);
     try {
-      final ok = await ReplayGainService.applyToFile(
-        item.filePath,
-        onUnsupportedDecoder: () => unsupportedDecoder = true,
-      );
+      final ok = remove
+          ? await ReplayGainService.removeFromFile(item.filePath)
+          : await ReplayGainService.applyToFile(
+              item.filePath,
+              onUnsupportedDecoder: () => unsupportedDecoder = true,
+            );
       if (ok) successCount++;
     } catch (_) {}
   }
@@ -618,7 +633,9 @@ Future<void> runBatchReplayGain(
     SnackBar(
       content: Text(
         [
-          context.l10n.replayGainBatchSuccess(successCount, total),
+          remove
+              ? context.l10n.replayGainRemoveBatchSuccess(successCount, total)
+              : context.l10n.replayGainBatchSuccess(successCount, total),
           if (unsupportedDecoder) context.l10n.replayGainUnsupportedDecoder,
         ].join('\n'),
       ),

lib/services/replaygain_service.dart

@@ -7,7 +7,7 @@ import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/utils/file_access.dart';
 import 'package:spotiflac_android/utils/logger.dart';
 
-/// Standalone ReplayGain (re)scanning for existing audio files.
+/// ReplayGain scanning and tag removal for existing audio files.
 ///
 /// Computes EBU R128 loudness via FFmpeg and writes gain tags using the native
 /// metadata editors where supported. Opus uses R128_* rather than legacy tags.
@@ -104,6 +104,33 @@ class ReplayGainService {
     (path) => _writeLocalTags(path, gain, peak, album: true),
   );
 
+  /// Removes track/album tags, including Opus R128 and M4A Sound Check tags.
+  /// Native editors copy the audio payload unchanged and publish atomically.
+  static Future<bool> removeFromFile(String filePath) =>
+      _updateFile(filePath, (path) async {
+        if (!_isNativeWritableFormat(path)) return false;
+        const fields = {
+          'replaygain_track_gain': '',
+          'replaygain_track_peak': '',
+          'replaygain_album_gain': '',
+          'replaygain_album_peak': '',
+        };
+        final result = await PlatformBridge.editFileMetadata(path, fields);
+        final method = result['method'];
+        if (result['success'] != true ||
+            result['error'] != null ||
+            method is! String ||
+            !(method == 'native' || method.startsWith('native_'))) {
+          return false;
+        }
+        final metadata = await PlatformBridge.readFileMetadata(path);
+        return metadata['error'] == null &&
+            metadata['audio_codec'] != null &&
+            fields.keys.every(
+              (key) => (metadata[key]?.toString() ?? '').trim().isEmpty,
+            );
+      });
+
   static Future<bool> _writeLocalTags(
     String path,
     String gain,
@@ -182,7 +209,7 @@ class ReplayGainService {
       if (isSaf) {
         safTempPath = await PlatformBridge.copyContentUriToTemp(filePath);
         if (safTempPath == null || safTempPath.isEmpty) {
-          _log.w('Failed to copy SAF file to temp for ReplayGain scan');
+          _log.w('Failed to copy SAF file to temp for ReplayGain update');
           return false;
         }
         workingPath = safTempPath;
@@ -199,10 +226,10 @@ class ReplayGainService {
       }
 
       refreshPlaybackNormalization(filePath);
-      _log.i('ReplayGain tags written and verified: $filePath');
+      _log.i('ReplayGain tags updated and verified: $filePath');
       return true;
     } catch (e) {
-      _log.e('Failed to apply ReplayGain', e);
+      _log.e('Failed to update ReplayGain', e);
       return false;
     } finally {
       if (safTempPath != null) {