fix: add missing imports and safety checks to Horizon/Pulse gates

app/Providers/AppServiceProvider.php

@@ -2,6 +2,8 @@
 
 namespace App\Providers;
 
+use App\Models\User;
+use Illuminate\Support\Facades\Gate;
 use Illuminate\Support\ServiceProvider;
 
 class AppServiceProvider extends ServiceProvider

app/Providers/HorizonServiceProvider.php

@@ -28,7 +28,7 @@ class HorizonServiceProvider extends HorizonApplicationServiceProvider
     protected function gate(): void
     {
         Gate::define('viewHorizon', function ($user = null) {
-            return $user->isAdmin();
+            return $user && $user->isAdmin();
         });
     }
 }