Add saved payout destination UX and service contracts (#54)

frontend/packages/sxchnge_wallet/README.md

@@ -47,3 +47,17 @@ once on success/failure. Closing the app while pending does not count as draft
 abandonment. No amounts, account IDs or recipient data enter events. All demo
 signals are simulated. Cross-session outcomes require backend event delivery;
 client-only analytics are not production accounting or conversion evidence.
+
+## Saved destinations — #54
+
+The injectable `DestinationService` adds canonical crypto, secure-card capture and
+Russian bank models, saved/one-time input, independent metadata/execution revisions,
+stable created/duplicate outcomes, contextual eligibility and management providers.
+`DummyDestinationService` is customer-scoped and process-local. It has isolated
+fixtures for directory/capture/recovery states, not live banking or card collection.
+The demo wallet binds immutable destination snapshots to quotes and rechecks at its
+synchronous acceptance boundary. Production must enforce those checks atomically
+in the backend. Live mode currently advertises no new destination capabilities and
+preserves explicit selection of the already provisioned wallet method. It never
+uses a demo store. See [the UX/service contract](../../../docs/ux/payout-destinations.md)
+for integration, security, retention, localization and acceptance requirements.