fix: non-primary CustomScrollViews in IndexedStack tabs

lib/screens/downloads/downloads_screen.dart

@@ -136,6 +136,7 @@ class DownloadsScreenState extends State<DownloadsScreen> with TickerProviderSta
   Widget build(BuildContext context) {
     return Scaffold(
       body: CustomScrollView(
+        primary: false,
         slivers: [
           DesktopSliverAppBar(
             title: _buildAppBarTitle(),

lib/screens/search_screen.dart

@@ -226,6 +226,7 @@ class _SearchScreenState extends State<SearchScreen> with Refreshable, FullRefre
     return Scaffold(
       body: SafeArea(
         child: CustomScrollView(
+          primary: false,
           slivers: [
             DesktopSliverAppBar(title: Text(t.common.search), floating: true),
             SliverToBoxAdapter(

lib/screens/settings/settings_screen.dart

@@ -238,6 +238,7 @@ class _SettingsScreenState extends State<SettingsScreen> with FocusableTab {
       body: Focus(
         onKeyEvent: _handleKeyEvent,
         child: CustomScrollView(
+          primary: false,
           slivers: [
             ExcludeFocus(child: CustomAppBar(title: Text(t.settings.title), pinned: true)),
             SliverPadding(