feat(packages): add standalone auth and payment

packages/payment/src/payment.models.ts

@@ -0,0 +1,18 @@
+export type PaymentMethod = 'qr' | 'card' | 'sbp' | 'yandex-pay';
+export type PaymentStatus = 'created' | 'pending' | 'authorized' | 'paid' | 'failed' | 'cancelled' | 'expired';
+/** Central payment API resolves amount/currency/routing from this server checkout id. */
+export interface PaymentRequest { checkoutSessionId: string; returnUrl?: string; metadata?: Readonly<Record<string, string>>; }
+export interface PaymentAttempt {
+  paymentId: string;
+  method: PaymentMethod;
+  status: PaymentStatus;
+  action?: { type: 'redirect' | 'qr'; url: string };
+  failureMessage?: string;
+}
+export interface PaymentResult extends PaymentAttempt { status: 'paid' | 'authorized'; }
+export interface PaymentFailure {
+  method: PaymentMethod;
+  code: 'configuration' | 'backend' | 'declined' | 'expired' | 'popup_blocked';
+  message: string;
+  cause?: unknown;
+}