feat: select mobile updates to mark read (Closes #545)

frontend/index.html

@@ -116,6 +116,11 @@
         </div>
       </details>
     </div>
+    <div class="update-selection-controls" id="update-selection-controls" hidden>
+      <button id="select-updates" type="button">Select updates</button>
+      <button id="cancel-update-selection" type="button" hidden>Cancel selection</button>
+      <span class="small" id="update-selection-status" role="status" aria-live="polite"></span>
+    </div>
     <div class="my-work-list" id="my-work-list"></div>
     <div class="small" id="work-page-status" aria-live="polite"></div>
     <button class="load-more-work" id="load-more-work" type="button" hidden>Load older work</button>