changed color theme to be black and added the ability to enter the amount in the recipient’s currency

frontend/pshared/lib/provider/payment/amount.dart

@@ -1,12 +1,15 @@
 import 'package:flutter/material.dart';
 
+import 'package:pshared/models/payment/settlement_mode.dart';
 
 class PaymentAmountProvider with ChangeNotifier {
   double _amount = 10.0;
   bool _payerCoversFee = true;
+  SettlementMode _settlementMode = SettlementMode.fixSource;
 
   double get amount => _amount;
   bool get payerCoversFee => _payerCoversFee;
+  SettlementMode get settlementMode => _settlementMode;
 
   void setAmount(double value) {
     _amount = value;
@@ -17,4 +20,10 @@ class PaymentAmountProvider with ChangeNotifier {
     _payerCoversFee = value;
     notifyListeners();
   }
+
+  void setSettlementMode(SettlementMode value) {
+    if (_settlementMode == value) return;
+    _settlementMode = value;
+    notifyListeners();
+  }
 }