feat(payment): configure named gateway providers

packages/payment/README.md

@@ -5,3 +5,27 @@ Gateway-neutral, webhook-authoritative payments for WrNexus. Amounts are integer
 Built-in adapters: offline `sandbox`, Stripe, Razorpay, and PayPal. Applications may add adapters with `defineGateway`. Capabilities are explicit, unsupported operations are refused, signed webhooks are mandatory in production, and package-owned migrations provision the append-only event ledger.
 
 Webhook events are deduplicated by the provider's event ID and reduced in provider occurrence/sequence order. Captured and refund states are monotonic, so a delayed retry of an older event cannot regress a terminal payment.
+
+Configure any number of named gateway accounts in `wrnexus.config.ts`; keep credentials in environment variables:
+
+```ts
+const payment = {
+  default: "razorpayIndia",
+  gateways: {
+    razorpayIndia: {
+      provider: "razorpay",
+      keyId: process.env.RAZORPAY_KEY_ID!,
+      keySecret: process.env.RAZORPAY_KEY_SECRET!,
+      webhookSecret: process.env.RAZORPAY_WEBHOOK_SECRET ?? "",
+    },
+    stripeGlobal: {
+      provider: "stripe",
+      secretKey: process.env.STRIPE_SECRET_KEY!,
+      publishableKey: process.env.STRIPE_PUBLISHABLE_KEY!,
+      webhookSecret: process.env.STRIPE_WEBHOOK_SECRET!,
+    },
+  },
+} satisfies PaymentConfig;
+```
+
+At runtime, call `configurePaymentFromConfig(config.payment, databasePaymentStore())` once. Pass a configured gateway name to `initializePayment` to override the default for a specific checkout.