feat : 테이블 및 DB 마이그레이션 파일 추가

products
  - common_codes
  - parts
  - products
  - files
  - price_histories
  - boms
  - bom_items

  boards
  - boards
  - board_settings
  - posts
  - board_comments
  - board_files
  - post_custom_field_values

  permissions
  - menus
  - roles
  - user_menu_permissions
  - role_menu_permissions

  tenants
  - tenants
  - plans
  - subscriptions
  - payments

app/Models/Menu.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+
+class Menu extends Model
+{
+    protected $fillable = [
+        'tenant_id', 'parent_id', 'name', 'url', 'is_active', 'sort_order',
+        'hidden', 'is_external', 'external_url', 'icon'
+    ];
+
+    public function parent()
+    {
+        return $this->belongsTo(Menu::class, 'parent_id');
+    }
+
+    public function children()
+    {
+        return $this->hasMany(Menu::class, 'parent_id');
+    }
+}