added wallet source to quotation preparation

frontend/pshared/lib/service/payment/wallets.dart

@@ -0,0 +1,27 @@
+import 'package:pshared/data/mapper/wallet/ui.dart';
+import 'package:pshared/models/payment/wallet.dart';
+import 'package:pshared/service/wallet.dart' as shared_wallet_service;
+
+
+abstract class WalletsService {
+  Future<List<Wallet>> getWallets(String organizationRef);
+  Future<double> getBalance(String organizationRef, String walletRef);
+}
+
+class ApiWalletsService implements WalletsService {
+  @override
+  Future<List<Wallet>> getWallets(String organizationRef) async {
+    final models = await shared_wallet_service.WalletService.list(organizationRef);
+    return models.map((m) => m.toUi()).toList();
+  }
+
+  @override
+  Future<double> getBalance(String organizationRef, String walletRef) async {
+    final balance = await shared_wallet_service.WalletService.getBalance(
+      organizationRef: organizationRef,
+      walletRef: walletRef,
+    );
+    final amount = balance.available?.amount;
+    return amount == null ? 0 : double.tryParse(amount) ?? 0;
+  }
+}