add set persistence

backend/database/migrations/2026_08_03_000000_create_sets_table.php

@@ -0,0 +1,24 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('sets', function (Blueprint $table): void {
+            $table->id();
+            $table->string('name')->unique();
+            $table->foreignId('creator_id')
+                ->constrained('users')
+                ->restrictOnDelete();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('sets');
+    }
+};