add admin user management: list and delete registered users

sentence_api/static/admin.html

@@ -71,6 +71,29 @@
       </div>
       <div id="empty-state" class="empty-state" hidden>暂无视频</div>
     </section>
+
+    <section class="video-band" aria-labelledby="users-heading">
+      <div class="section-heading">
+        <h2 id="users-heading">用户管理</h2>
+        <span id="user-count">0 个用户</span>
+      </div>
+      <div class="table-scroll">
+        <table>
+          <thead>
+            <tr>
+              <th>用户名</th>
+              <th>姓名</th>
+              <th>手机号</th>
+              <th>选修课程</th>
+              <th>注册时间</th>
+              <th class="actions-column">操作</th>
+            </tr>
+          </thead>
+          <tbody id="user-rows"></tbody>
+        </table>
+      </div>
+      <div id="user-empty-state" class="empty-state" hidden>暂无用户</div>
+    </section>
   </main>
 
   <dialog id="sentence-dialog">