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

frontend/app/lib/destinations/details.dart

@@ -0,0 +1,41 @@
+import 'package:flutter/material.dart';
+
+import 'package:sxchnge_wallet/sxchnge_wallet.dart';
+
+import '../generated/i18n/app_localizations.dart';
+
+/// Structured review renders the immutable service snapshot, never a nickname.
+class DestinationDetailsView extends StatelessWidget {
+  const DestinationDetailsView({super.key, required this.details});
+  final DestinationDetails details;
+  Widget field(String label, String value) => Padding(
+    padding: const EdgeInsets.only(top: 12),
+    child: Column(
+      crossAxisAlignment: CrossAxisAlignment.stretch,
+      children: [Text(label), SelectableText(value)],
+    ),
+  );
+  @override
+  Widget build(BuildContext context) {
+    final l = AppLocalizations.of(context)!;
+    return Column(
+      crossAxisAlignment: CrossAxisAlignment.stretch,
+      children: switch (details) {
+        CryptoDestination d => [
+          field(l.dAsset, d.assetLabel),
+          field(l.dNetwork, d.networkLabel),
+          field(l.dAddress, d.address),
+          field(l.dMemo, d.memo.isEmpty ? l.dNoMemo : d.memo),
+        ],
+        CardDestination d => [field(l.dCard, d.display)],
+        RussianBankDestination d => [
+          field(l.dHolder, d.holder),
+          field(l.dBankSearch, d.bank.name),
+          field(l.dBik, d.bank.bik),
+          field(l.dAccount, d.account),
+          field(l.dCorrespondent, d.bank.correspondent),
+        ],
+      },
+    );
+  }
+}