Defer rendering of mini-message components for optimized loading using viewport and idle prefetch placeholders.

frontend/src/app/pages/altitude/chat/components/chat/chat-box.component.html

@@ -4,7 +4,11 @@
       <span class="date-time" [class.blocked]="!message.notBlocked">
         [{{ message.timestamp | date: 'mediumTime' }}]
       </span>
+      @defer (on viewport; prefetch on idle) {
         <mini-message [node]="message.messageJson"></mini-message>
+      } @placeholder {
+        <span>…</span>
+      }
     </p>
   }
 </div>