feat: 下载时若存在数据丢失风险则弹窗提示；服务端增加占用信息查看功能

client/lib/utils.dart

@@ -4,6 +4,7 @@ import 'package:archive/archive_io.dart';
 import 'package:cloud_archiver/config.dart';
 import 'package:cloud_archiver/state.dart';
 import 'package:filesize/filesize.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:path/path.dart';
 import 'package:path_provider/path_provider.dart';
@@ -24,7 +25,7 @@ String totalSize() {
 Future<bool> connect(String server, String user, String auth) async {
   var client = dav.newClient(
     server,
-    debug: true,
+    debug: kDebugMode,
     user: user,
     password: auth,
   );