add user service and update user model for customer details retrieval

lib/api/services/customer_service.dart

@@ -0,0 +1,28 @@
+import 'package:dio/dio.dart';
+import 'package:flutter/foundation.dart';
+import 'package:kmobile/data/models/user.dart';
+
+class UserService {
+  final Dio _dio;
+  UserService(this._dio);
+
+  Future<List<User>> getUserDetails(String customerNo) async {
+    try {
+      final response = await _dio.get('/customer/details');
+      if (response.statusCode == 200) {
+        return (response.data as List)
+            .map((user) => User.fromJson(user))
+            .toList();
+      } else {
+        throw Exception('Failed to load customer details');
+      }
+    } on DioException catch (e) {
+      if (kDebugMode) {
+        print(e.toString());
+      }
+      throw Exception('Network error: ${e.message}');
+    } catch (e) {
+      throw Exception('Unexpected error: ${e.toString()}');
+    }
+  }
+}