feat: open updates at newest activity (Closes #759)

frontend/index.html

@@ -760,6 +760,7 @@
     </div>
     <h2>Full conversation</h2>
     <div id="update-comments"></div>
+    <button class="update-new-activity-jump" id="jump-update-new-activity" type="button" hidden>Jump to new activity</button>
     <button class="conversation-more" id="load-older-update-comments" type="button" hidden>Load older messages</button>
     <div id="update-conversation-status" class="small" aria-live="assertive"></div>
     <details>
@@ -1074,6 +1075,7 @@
 <script src="static/mobile-work-entry.js"></script>
 <script src="static/mobile-queue-launcher.js"></script>
 <script src="static/update-triage-session.js"></script>
+<script src="static/update-read-position.js"></script>
 <script src="static/update-triage-launcher.js"></script>
 <script src="static/agenda-session-launcher.js"></script>
 <script src="static/mobile-launch.js"></script>