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/payhere.provider.js

@@ -0,0 +1,5 @@
+const crypto=require("crypto"),md5=x=>crypto.createHash("md5").update(String(x)).digest("hex").toUpperCase();
+function verifyWebhook(p){const secret=process.env.PAYHERE_MERCHANT_SECRET;if(!secret)return false;const expected=md5(`${p.merchant_id}${p.order_id}${p.payhere_amount}${p.payhere_currency}${p.status_code}${md5(secret)}`),actual=String(p.md5sig||"").toUpperCase().padEnd(expected.length,"0").slice(0,expected.length);return crypto.timingSafeEqual(Buffer.from(expected),Buffer.from(actual));}
+function parseWebhook(p){return{eventId:p.payment_id||`${p.order_id}:${p.status_code}:${p.payhere_amount}`,paymentReference:p.order_id,providerTransactionId:p.payment_id,status:String(p.status_code)==="2"?"PAID":String(p.status_code)==="0"?"PENDING":"FAILED",amount:String(p.payhere_amount),currency:p.payhere_currency,eventType:`PAYHERE_${p.status_code}`};}
+function createPayment({reference,amount,currency}){const merchantId=process.env.PAYHERE_MERCHANT_ID,secret=process.env.PAYHERE_MERCHANT_SECRET;if(!merchantId||!secret)throw Object.assign(new Error("PayHere is not configured"),{code:"PROVIDER_NOT_CONFIGURED",status:503});return{merchant_id:merchantId,order_id:reference,amount,currency,hash:md5(`${merchantId}${reference}${amount}${currency}${md5(secret)}`),notify_url:process.env.PAYHERE_NOTIFY_URL,return_url:process.env.PAYHERE_RETURN_URL,cancel_url:process.env.PAYHERE_CANCEL_URL};}
+const unavailable=()=>{throw Object.assign(new Error("Provider operation is not configured"),{code:"PROVIDER_OPERATION_UNAVAILABLE",status:503});};module.exports={createPayment,verifyWebhook,parseWebhook,refund:unavailable,getPaymentStatus:unavailable};

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};