feat: expose Updates in mobile queues (Closes #639)

frontend/index.html

@@ -861,6 +861,7 @@
     <div class="mobile-queue-list">
       <button data-mobile-queue="today" type="button"><span><strong>Today</strong><small>Planned work</small></span><span data-mobile-queue-count="today">0</span></button>
       <button data-mobile-queue="attention" type="button"><span><strong>Attention</strong><small>Needs a response</small></span><span data-mobile-queue-count="attention">0</span></button>
+      <button data-mobile-queue="update" type="button" aria-label="Updates, 0 unread conversations"><span><strong>Updates</strong><small>Unread conversations</small></span><span data-mobile-queue-count="update">0</span></button>
       <button data-mobile-queue="later" type="button"><span><strong>Later</strong><small>Deferred work</small></span><span data-mobile-queue-count="later">0</span></button>
       <button data-mobile-queue="draft" type="button"><span><strong>Drafts</strong><small>Unfiled captures</small></span><span data-mobile-queue-count="draft">0</span></button>
     </div>