Use unique reference_id for Razorpay payment links

src/main/kotlin/com/android/trisolarisserver/controller/RazorpayPaymentLinksController.kt

@@ -93,7 +93,8 @@ class RazorpayPaymentLinksController(
             "currency" to currency,
             "description" to (request.description ?: "Booking $bookingId"),
             "notes" to notes,
-            "reference_id" to bookingId.toString()
+            // Razorpay requires reference_id to be unique per active link
+            "reference_id" to "${bookingId}-${OffsetDateTime.now().toEpochSecond()}"
         )
         parseExpiryEpoch(request.expiryDate)?.let { payload["expire_by"] = it }
         request.isPartialPaymentAllowed?.let { payload["partial_payment"] = it }