fix: products 테이블 category_id nullable로 변경

- 외래 키 제약조건으로 인한 INSERT 오류 해결
- category_id 기본값 null 설정
- ON DELETE SET NULL로 외래 키 제약조건 변경

database/migrations/2025_12_02_163431_alter_products_table_category_id_nullable.php

@@ -0,0 +1,51 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('products', function (Blueprint $table) {
+            // 기존 외래 키 제약조건 삭제
+            $table->dropForeign(['category_id']);
+        });
+
+        Schema::table('products', function (Blueprint $table) {
+            // category_id를 nullable로 변경하고 기본값 null 설정
+            $table->unsignedBigInteger('category_id')->nullable()->default(null)->change();
+
+            // 외래 키 재설정 (SET NULL)
+            $table->foreign('category_id')
+                ->references('id')
+                ->on('categories')
+                ->onDelete('set null')
+                ->onUpdate('cascade');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('products', function (Blueprint $table) {
+            $table->dropForeign(['category_id']);
+        });
+
+        Schema::table('products', function (Blueprint $table) {
+            $table->unsignedBigInteger('category_id')->nullable(false)->default(0)->change();
+
+            $table->foreign('category_id')
+                ->references('id')
+                ->on('categories')
+                ->onDelete('restrict')
+                ->onUpdate('cascade');
+        });
+    }
+};