<div class="d-flex flex-column align-items-center justify-content-center h-100 text-muted" style="min-height:400px;">
  <span class="bi bi-chat-square-dots" style="font-size:3rem;color:#cbd5e1;margin-bottom:16px;"></span>
  <p class="fw-semibold mb-1" style="color:#64748b;">Select a conversation</p>
  <p style="font-size:.85rem;color:#94a3b8;">Select a conversation on the left to view messages</p>
</div>
