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/payment/src/Factories/PaymentGatewayFactory.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace Modules\Payment\Factories;
+
+use Modules\Payment\Contracts\PaymentGatewayInterface;
+use Modules\Payment\Enums\PaymentMethod;
+use RuntimeException;
+
+/**
+ * Resolves a PaymentGatewayInterface implementation by PaymentMethod.
+ *
+ * Replaces bnf_event's 3x duplicated `switch($payment_type)` at each call
+ * site (domain.md §6). Call sites depend only on this factory, never on a
+ * concrete gateway class — swapping/adding a gateway is a `register()` call
+ * here, no controller/action changes.
+ */
+class PaymentGatewayFactory
+{
+    /**
+     * @var array<string, class-string<PaymentGatewayInterface>>
+     */
+    private array $bindings = [];
+
+    /**
+     * @param  class-string<PaymentGatewayInterface>  $gatewayClass
+     */
+    public function register(PaymentMethod $method, string $gatewayClass): void
+    {
+        $this->bindings[$method->value] = $gatewayClass;
+    }
+
+    public function make(PaymentMethod $method): PaymentGatewayInterface
+    {
+        $gatewayClass = $this->bindings[$method->value]
+            ?? throw new RuntimeException("No payment gateway registered for method [{$method->value}].");
+
+        return app($gatewayClass);
+    }
+}