feat: add Flutter mobile clients and staff delivery API

apps/user_app/test/domain/client_models_test.dart

@@ -0,0 +1,11 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:user_app/domain/models/client_models.dart';
+
+void main() {
+  group('moneyText', () {
+    test('formats minor currency units', () {
+      expect(moneyText(12345), '¥123.45');
+      expect(moneyText(0), '¥0.00');
+    });
+  });
+}