feat(macos): support start in fullscreen setting

close #1200

lib/main.dart

@@ -228,10 +228,10 @@ Future<void> _bootstrapApp() async {
 
   FullscreenStateManager().startMonitoring();
 
-  // Apply "start in fullscreen" preference on Windows/Linux. macOS is
-  // excluded — its native fullscreen animation is awkward at launch and
-  // the OS already restores window state.
-  if ((Platform.isWindows || Platform.isLinux) && settings.read(SettingsService.startInFullscreen)) {
+  // Apply "start in fullscreen" preference on desktop. macOS does not restore
+  // fullscreen state on its own (frame autosave only persists windowed geometry),
+  // so it needs the same explicit handling as Windows/Linux.
+  if (PlatformDetector.isDesktopOS() && settings.read(SettingsService.startInFullscreen)) {
     unawaited(FullscreenStateManager().enterFullscreen());
   }
 

lib/screens/settings/appearance_settings_screen.dart

@@ -115,7 +115,7 @@ class AppearanceSettingsScreen extends StatelessWidget {
           subtitle: t.settings.showUnwatchedCountDescription,
         ),
 
-        if (Platform.isWindows || Platform.isLinux) ...[
+        if (PlatformDetector.isDesktopOS()) ...[
           SettingsSectionHeader(t.settings.window),
           SettingSwitchTile(
             pref: SettingsService.startInFullscreen,
@@ -123,10 +123,6 @@ class AppearanceSettingsScreen extends StatelessWidget {
             title: t.settings.startInFullscreen,
             subtitle: t.settings.startInFullscreenDescription,
           ),
-        ],
-
-        if (PlatformDetector.isDesktopOS()) ...[
-          if (!(Platform.isWindows || Platform.isLinux)) SettingsSectionHeader(t.settings.window),
           SettingSwitchTile(
             pref: SettingsService.exitFullscreenOnPlayerClose,
             icon: Symbols.fullscreen_exit_rounded,