Restore missing HtmlString import in UserPanelProvider

Accidentally removed when cleaning up login render hook; still needed
for the sidebar footer build-info hook.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Providers/Filament/UserPanelProvider.php

@@ -4,6 +4,7 @@ namespace App\Providers\Filament;
 
 use Filament\Navigation\NavigationGroup;
 use Filament\View\PanelsRenderHook;
+use Illuminate\Support\HtmlString;
 use Filament\Http\Middleware\Authenticate;
 use Filament\Http\Middleware\DisableBladeIconComponents;
 use Filament\Http\Middleware\DispatchServingFilamentEvent;