feat: Implement return and refund functionality in commerce module

- Added return request handling in return.controller.js
- Implemented webhook handling for PayHere payments in webhook.controller.js
- Created models for coupon redemptions, invoices, orders, order items, payments, payment attempts, payment webhook events, refunds, return items, and return requests.
- Developed services for order management, payment processing, refunds, and returns.
- Introduced validation schemas for payment and return requests.
- Created migration scripts for new database tables related to orders, payments, refunds, and returns.
- Added unit tests for order state transitions and PayHere provider functionality.

app/services/commerce/providers/stripe.provider.js

@@ -0,0 +1 @@
+const unavailable=()=>{throw Object.assign(new Error("Stripe adapter is disabled until the official SDK and webhook secret are configured"),{code:"PROVIDER_NOT_CONFIGURED",status:503});};module.exports={createPayment:unavailable,verifyWebhook:()=>false,parseWebhook:unavailable,refund:unavailable,getPaymentStatus:unavailable};