New yotpo_customer_id field in customer responses

Customer responses now include yotpo_customer_id, the customer's internal Yotpo Loyalty ID.

Where it's returned:

• Fetch Customer Details (GET /api/v2/customers)
• Fetch All Recently Updated Customers (GET /api/v2/customers/recent)

Why it matters: This is the same ID shown in the customer page URL in the Loyalty admin. You can now get it through the API and use it with Loyalty endpoints that take an internal customer ID, without an admin lookup.

The field is an integer and has been added alongside the existing fields, so current integrations aren't affected.