Experimental mpv-style (uosc) controls behind a Settings toggle

Thick timeline with hatched cache range, chapter diamonds and
chapter/time hover boxes; collapses to a thin progress line when
hidden. Flat icon row with track count badges, shader preset badge,
flat dark menus. Own show/hide state, live switch in window and
fullscreen. New buffered signal from demuxer-cache-time.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/lib/src/screens/home/settings_page.dart

@@ -37,7 +37,13 @@ class SettingsPage extends StatelessWidget {
       children: [
         const PageTitle('Settings'),
         const _Section(title: 'Profile', child: ProfileEditor()),
-        const _Section(title: 'Player', child: _HwdecSetting()),
+        const _Section(
+          title: 'Player',
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.stretch,
+            children: [_HwdecSetting(), SizedBox(height: 12), _MpvControlsSetting()],
+          ),
+        ),
         const _Section(title: 'Jellyfin', child: _AutoAdvanceSetting()),
         _Section(title: 'Updates', child: _UpdateSettings(controller: updates)),
         const _Section(title: 'Keyboard shortcuts', child: _ShortcutList()),
@@ -295,6 +301,26 @@ class _UpdateSettings extends StatelessWidget {
   }
 }
 
+class _MpvControlsSetting extends StatelessWidget {
+  const _MpvControlsSetting();
+
+  @override
+  Widget build(BuildContext context) {
+    final s = AppSettings.instance;
+    return SignalBuilder(
+      builder: (context) => SwitchListTile(
+        key: const ValueKey('mpv-controls'),
+        contentPadding: EdgeInsets.zero,
+        title: const Text('Experimental: mpv-style controls'),
+        subtitle: const Text('Video controls modeled on mpv\'s uosc theme: a thick timeline with '
+            'chapters and the cached range, flat buttons and menus. Applies right away.'),
+        value: s.mpvControls.value,
+        onChanged: s.setMpvControls,
+      ),
+    );
+  }
+}
+
 class _AutoAdvanceSetting extends StatelessWidget {
   const _AutoAdvanceSetting();