Add Payment module: contracts, payments/refunds tables, KBZ gateway, factory, orchestrator (T5.1-T5.7)

- T5.1 PaymentGatewayInterface, DTOs, PaymentMethod/PaymentStatus/RefundStatus enums
- T5.2 payments/refunds tables, models, factories
- T5.3-T5.5 KbzMiniAppGateway: initiate()/verify()/refund(), ported KBZ signing scheme,
  wired refund_amount through for partial refunds, mTLS options for refund
- T5.6 PaymentGatewayFactory resolving gateways by PaymentMethod
- T5.7 PaymentService orchestrator delegating to the resolved gateway

app-modules/booking/src/Models/Booking.php

@@ -11,6 +11,7 @@ use Modules\Booking\Database\Factories\BookingFactory;
 use Modules\Booking\Enums\BookingChannel;
 use Modules\Booking\Enums\BookingStatus;
 use Modules\Catalog\Models\DepartureTimeSlot;
+use Modules\Payment\Models\Payment;
 use Modules\Routing\Models\EvRoute;
 
 class Booking extends Model
@@ -85,4 +86,9 @@ class Booking extends Model
     {
         return $this->hasMany(BookingVehicleOption::class);
     }
+
+    public function payments(): HasMany
+    {
+        return $this->hasMany(Payment::class);
+    }
 }