feat: reply to updates and continue Today (#451)

frontend/index.html

@@ -466,7 +466,10 @@
       <textarea id="update-reply" maxlength="10000" placeholder="Write a reply"></textarea>
       <div class="mention-options" id="update-reply-mentions" role="listbox" aria-label="Teammates" hidden></div>
       <div class="mention-status small" id="update-reply-mention-status" aria-live="polite"></div>
-      <button id="send-update-reply" type="button">Send reply</button>
+      <div class="update-reply-actions">
+        <button id="send-update-reply" type="button">Send reply</button>
+        <button id="send-update-reply-next" type="button" hidden>Reply &amp; next</button>
+      </div>
       <div id="update-reply-status" class="small" aria-live="assertive"></div>
     </section>
     <div class="update-sheet-actions">