feat: mention teammates from Today updates (Closes #1064)

frontend/index.html

@@ -1558,6 +1558,8 @@
     </section>
     <label for="today-progress-body">Update</label>
     <textarea id="today-progress-body" rows="5" maxlength="2000" placeholder="What changed, what you learned, or what comes next"></textarea>
+    <div class="mention-options" id="today-progress-body-mentions" role="listbox" aria-label="Teammates" hidden></div>
+    <div class="mention-status small" id="today-progress-body-mention-status" aria-live="polite"></div>
     <section class="voice-conversation" id="voice-today-progress" data-draft-label="progress update" aria-label="Dictate Today progress update" hidden>
       <div class="voice-conversation-controls">
         <button id="start-voice-today-progress" type="button">Dictate update</button>