feat: 實作 POS API 整合功能，包含商品與銷售訂單同步及韌性機制

app/Modules/Integration/Models/SalesOrder.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Modules\Integration\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+class SalesOrder extends Model
+{
+    protected $table = 'sales_orders';
+
+    protected $fillable = [
+        'external_order_id',
+        'status',
+        'payment_method',
+        'total_amount',
+        'sold_at',
+        'raw_payload',
+    ];
+
+    protected $casts = [
+        'sold_at' => 'datetime',
+        'raw_payload' => 'array',
+        'total_amount' => 'decimal:4',
+    ];
+
+    public function items(): HasMany
+    {
+        return $this->hasMany(SalesOrderItem::class);
+    }
+}