Require Ladill Pay only for Merchant checkouts.

Remove custom/owner payment gateway option and always route customer payments through Ladill Pay with platform fees.

app/Services/Billing/PlanEntitlementService.php

@@ -22,6 +22,8 @@ class PlanEntitlementService
 
     public function canUseCustomPaymentGateway(User $owner): bool
     {
-        return $this->has($owner, self::CUSTOM_PAYMENT_GATEWAY);
+        // Custom / owner payment gateways are retired. All checkouts use Ladill Pay
+        // with platform fees (see config/pay.php fee_tiers on the platform).
+        return false;
     }
 }