fix(test): 测试用例添加 simple_mode 字段

API 响应新增 simple_mode 字段，同步更新测试期望值

backend/internal/server/api_contract_test.go

@@ -280,6 +280,7 @@ func TestAPIContracts(t *testing.T) {
 
 					service.SettingKeyDefaultConcurrency: "5",
 					service.SettingKeyDefaultBalance:     "1.25",
+					service.SettingKeySimpleMode:         "false",
 				})
 			},
 			method:     http.MethodGet,
@@ -308,7 +309,8 @@ func TestAPIContracts(t *testing.T) {
 					"contact_info": "support",
 					"doc_url": "https://docs.example.com",
 					"default_concurrency": 5,
-					"default_balance": 1.25
+					"default_balance": 1.25,
+					"simple_mode": false
 				}
 			}`,
 		},