add set persistence

backend/app/Set/Set.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Set;
+
+use App\User\User;
+
+final readonly class Set
+{
+    public function __construct(
+        private int $id,
+        private string $name,
+        private User $creator,
+    ) {}
+
+    public function getId(): int
+    {
+        return $this->id;
+    }
+
+    public function getName(): string
+    {
+        return $this->name;
+    }
+
+    public function getCreator(): User
+    {
+        return $this->creator;
+    }
+}