Add extensive controller and model tests

tests/Feature/SystemStatusControllerTest.php

@@ -0,0 +1,13 @@
+<?php
+
+use App\Models\User;
+use Laravel\Sanctum\Sanctum;
+
+it('forbids system status for non-admins', function (): void {
+    $user = User::factory()->create();
+
+    Sanctum::actingAs($user);
+    $response = $this->getJson('/api/system/status');
+
+    $response->assertStatus(403);
+});