引入sweetalert代替alert；用户注册密码长度及字符校验；注册页前端显示密码策略及样式优化；字体渲染显示网页逻辑调整；后端添加40004错误码

bookshelfplus-frontend/views/component/header.html

@@ -8,6 +8,9 @@
 <script src="/assets/lib/jquery/3.6.0/jquery.min.js"></script>
 <script src="/assets/lib/axios/0.26.1/axios.min.js"></script>
 
+<!-- refer: https://www.sweetalert.cn/ -->
+<script src="/assets/lib/sweetalert/2.1.2/sweetalert.min.js"></script>
+
 <script src="/assets/javascripts/httpRequestUtils.js"></script>
 <script src="/assets/javascripts/localStorageUtils.js"></script>
 <script>
@@ -19,7 +22,6 @@
     /* 字体加载前先隐藏，不然文字会闪一下 */
     html, body { opacity: 0; }
 </style>
-
 <script>
     /**
      * 获取用户浏览器指纹