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

docs/implementation.md

@@ -968,3 +968,31 @@ remain separate capabilities. Unrelated notifications runtime changes are exclud
 Delivered in [PR #51](https://git.sendico.io/tech/sxchnge/pulls/51), targeting
 `identity-verification-48`. Merge order is #47 → #49 → #51; deploy Sendico #2897
 before SXCHNGE #51. Both implementation branches are pushed and remain unmerged.
+
+## Saved payout destinations UX — #54
+
+Branch `payout-destinations-54`, based on `local-stand-52`. Implements Settings
+creation, details, rename, replacement and removal; explicit payout selection;
+optional saving and one-time preparation for crypto, cards and Russian personal
+accounts. Shared typed service/model/provider layers separate destination identity,
+metadata/execution revisions, ownership, provider bindings, contextual eligibility,
+save outcomes and financial outcomes. The customer-scoped demo replays stable
+created/duplicate results, preserves immutable quote/history snapshots, rechecks at
+acceptance, and demonstrates card-binding restoration without creating a second
+card. Bank directory/paste handling follows the reviewed Sendico interface.
+
+EN/RU and 320 px/1.6× layouts are tested. Formatting (44 changed Dart files),
+analysis of app/wallet/analytics, `make test-frontend` (including 89 app tests), and
+`flutter build web` with Wasm dry run passed. Browser smoke inspection confirmed
+bank form rendering, labeled controls and keyboard focus. Full assistive-technology
+and real-provider audits were not performed. No security scans were requested/run.
+
+Persistence and bindings in this delivery are simulated and reset on reload.
+Authenticated live mode retains explicit use of its provisioned payout destination;
+new types fail closed until the backend supplies the documented capabilities and
+registry/atomic-acceptance contracts. No routing, ownership-verification system,
+provider integration or financial engine was added. See
+[the specification and integration boundary](ux/payout-destinations.md).
+
+Stacked merge order: #47 → #49 → #51 → #53 → this contribution. The unrelated
+notifications runtime edit is preserved outside task commits. Delivery links follow.