multiple payout page and small fixes

frontend/pshared/lib/utils/payment/fx_helpers.dart

@@ -0,0 +1,47 @@
+import 'package:pshared/models/payment/currency_pair.dart';
+import 'package:pshared/models/payment/fx/intent.dart';
+import 'package:pshared/models/payment/fx/side.dart';
+import 'package:pshared/models/money.dart';
+
+
+class FxIntentHelper {
+  static FxIntent? buildSellBaseBuyQuote({
+    required String baseCurrency,
+    required String quoteCurrency,
+    bool enabled = true,
+  }) {
+    if (!enabled) return null;
+    final base = baseCurrency.trim();
+    final quote = quoteCurrency.trim();
+    if (base.isEmpty || quote.isEmpty) return null;
+    if (base.toUpperCase() == quote.toUpperCase()) return null;
+    return FxIntent(
+      pair: CurrencyPair(base: base, quote: quote),
+      side: FxSide.sellBaseBuyQuote,
+    );
+  }
+
+  static String resolveSettlementCurrency({
+    required Money amount,
+    FxIntent? fx,
+  }) {
+    final pair = fx?.pair;
+    if (pair != null) {
+      switch (fx?.side ?? FxSide.unspecified) {
+        case FxSide.buyBaseSellQuote:
+          if (pair.base.isNotEmpty) return pair.base;
+          break;
+        case FxSide.sellBaseBuyQuote:
+          if (pair.quote.isNotEmpty) return pair.quote;
+          break;
+        case FxSide.unspecified:
+          break;
+      }
+      if (amount.currency == pair.base && pair.quote.isNotEmpty) return pair.quote;
+      if (amount.currency == pair.quote && pair.base.isNotEmpty) return pair.base;
+      if (pair.quote.isNotEmpty) return pair.quote;
+      if (pair.base.isNotEmpty) return pair.base;
+    }
+    return amount.currency;
+  }
+}