feat: add audio normalization toggle (MPV loudnorm filter)

lib/widgets/video_controls/sheets/video_settings_sheet.dart

@@ -129,6 +129,7 @@ class _VideoSettingsSheetState extends State<VideoSettingsSheet> {
   bool _showPerformanceOverlay = false;
   bool _autoPlayNextEpisode = true;
   bool _audioPassthrough = false;
+  bool _audioNormalization = false;
 
   @override
   void initState() {
@@ -146,6 +147,7 @@ class _VideoSettingsSheetState extends State<VideoSettingsSheet> {
       _showPerformanceOverlay = settings.getShowPerformanceOverlay();
       _autoPlayNextEpisode = settings.getAutoPlayNextEpisode();
       _audioPassthrough = settings.getAudioPassthrough();
+      _audioNormalization = settings.getAudioNormalization();
     });
   }
 
@@ -192,6 +194,17 @@ class _VideoSettingsSheetState extends State<VideoSettingsSheet> {
     await widget.player.setAudioPassthrough(newValue);
   }
 
+  Future<void> _toggleAudioNormalization() async {
+    final newValue = !_audioNormalization;
+    final settings = await SettingsService.getInstance();
+    await settings.setAudioNormalization(newValue);
+    if (!mounted) return;
+    setState(() {
+      _audioNormalization = newValue;
+    });
+    await widget.player.setProperty('af', newValue ? 'loudnorm=I=-14:TP=-3:LRA=4' : '');
+  }
+
   void _navigateTo(_SettingsView view) {
     // Sync views open as a compact top bar instead of a sub-view
     if (view == _SettingsView.audioSync || view == _SettingsView.subtitleSync) {
@@ -427,6 +440,23 @@ class _VideoSettingsSheetState extends State<VideoSettingsSheet> {
             onTap: _toggleAudioPassthrough,
           ),
 
+        // Audio Normalization (MPV only)
+        if (widget.player.playerType == 'mpv')
+          ListTile(
+            leading: AppIcon(
+              Symbols.graphic_eq_rounded,
+              fill: 1,
+              color: _audioNormalization ? Colors.amber : tokens(context).textMuted,
+            ),
+            title: Text(t.videoSettings.audioNormalization),
+            trailing: Switch(
+              value: _audioNormalization,
+              onChanged: (_) => _toggleAudioNormalization(),
+              activeThumbColor: Colors.amber,
+            ),
+            onTap: _toggleAudioNormalization,
+          ),
+
         // Shader Preset (MPV only)
         if (widget.shaderService != null && widget.shaderService!.isSupported)
           _SettingsMenuItem(