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/Models/Payment.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Modules\Payment\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+use Modules\Booking\Models\Booking;
+use Modules\Payment\Database\Factories\PaymentFactory;
+use Modules\Payment\Enums\PaymentMethod;
+use Modules\Payment\Enums\PaymentStatus;
+
+/**
+ * One attempt to pay for a Booking through a gateway — a Booking can have
+ * more than one Payment row if an earlier attempt failed and the customer
+ * retried (domain.md §1).
+ */
+class Payment extends Model
+{
+    /** @use HasFactory<PaymentFactory> */
+    use HasFactory;
+
+    /**
+     * @var list<string>
+     */
+    protected $fillable = [
+        'booking_id',
+        'gateway',
+        'status',
+        'amount',
+        'currency',
+        'gateway_transaction_id',
+        'gateway_payload',
+        'initiated_at',
+        'completed_at',
+    ];
+
+    /**
+     * @return array<string, string>
+     */
+    protected function casts(): array
+    {
+        return [
+            'gateway' => PaymentMethod::class,
+            'status' => PaymentStatus::class,
+            'amount' => 'decimal:2',
+            'gateway_payload' => 'array',
+            'initiated_at' => 'datetime',
+            'completed_at' => 'datetime',
+        ];
+    }
+
+    public function booking(): BelongsTo
+    {
+        return $this->belongsTo(Booking::class);
+    }
+
+    public function refunds(): HasMany
+    {
+        return $this->hasMany(Refund::class);
+    }
+}

app-modules/payment/src/Models/Refund.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace Modules\Payment\Models;
+
+use App\Models\User;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Modules\Payment\Database\Factories\RefundFactory;
+use Modules\Payment\Enums\RefundStatus;
+
+/**
+ * A reversal against a specific successful Payment (not against the Booking
+ * directly) — a Payment can have more than one Refund row for partial
+ * refunds (domain.md §1, §6).
+ */
+class Refund extends Model
+{
+    /** @use HasFactory<RefundFactory> */
+    use HasFactory;
+
+    /**
+     * @var list<string>
+     */
+    protected $fillable = [
+        'payment_id',
+        'status',
+        'amount',
+        'reason',
+        'gateway_refund_id',
+        'gateway_payload',
+        'requested_by',
+        'requested_at',
+        'completed_at',
+    ];
+
+    /**
+     * @return array<string, string>
+     */
+    protected function casts(): array
+    {
+        return [
+            'status' => RefundStatus::class,
+            'amount' => 'decimal:2',
+            'gateway_payload' => 'array',
+            'requested_at' => 'datetime',
+            'completed_at' => 'datetime',
+        ];
+    }
+
+    public function payment(): BelongsTo
+    {
+        return $this->belongsTo(Payment::class);
+    }
+
+    public function requestedBy(): BelongsTo
+    {
+        return $this->belongsTo(User::class, 'requested_by');
+    }
+}