feat:增加服务器接口模块

lib/apis/auth_api.dart

@@ -0,0 +1,11 @@
+import 'package:sweet_chat_app/models/auth.dart';
+import 'package:sweet_chat_app/services/dio_service.dart';
+
+Future<Auth> loginApi(String username, String password) async {
+  final res = await dioService.post(
+    '/auth/login',
+    data: {'username': username, 'password': password},
+  );
+
+  return Auth.fromJson(res.data);
+}