feat: add sequential Following review pass (Closes #1299)

frontend/index.html

@@ -2030,6 +2030,7 @@
   <section class="following-panel">
     <header><div><p class="small muted">Read without taking ownership</p><h2 id="following-title">Following</h2></div><button id="close-following" type="button">Close</button></header>
     <p id="following-status" class="small" role="status" aria-live="polite"></p>
+    <button id="review-following" class="following-review-action" type="button" hidden>Review new activity</button>
     <div id="following-list" class="following-list"></div>
     <button id="retry-following" type="button" hidden>Retry</button>
   </section>