add licensed random user creation flow

public/index.html

@@ -11,8 +11,12 @@
       <aside class="sidebar">
         <div class="sidebar-header">
           <p class="eyebrow">Microsoft 365</p>
-          <h1>邮箱控制台</h1>
+          <div class="sidebar-title-row">
+            <h1>邮箱控制台</h1>
+            <button id="create-user" type="button">随机建号</button>
+          </div>
           <p class="sidebar-copy">列出租户账号，点击后读取该账号收件箱中的最新一封邮件。</p>
+          <p id="sidebar-status" class="sidebar-status hidden"></p>
         </div>
 
         <label class="search-box" for="search-input">