message: Don't display action buttons on handled message cards
diff: <div class="cardstack-message-card" data-test-message-card>
  <div class="main-content">{{content.text}}</div>
  <div class="button-panel">
  + {{#unless content.isHandled}}
  <button type="button" class="action-button" data-test-approve-button onclick={{action 'approve'}}>
  Approve
  </button>
  <button type="button" class="action-button" data-test-deny-button onclick={{action 'deny'}}>
  Deny
  </button>
  + {{/unless}}
  </div>
  </div>
  \ No newline at end of file
  