Use "open" shadow root mode instead of "closed"

Style isolation still applies.

Co-authored-by: Robert Knight <robertknight@gmail.com>

h/static/scripts/group-forms/index.tsx

@@ -4,7 +4,7 @@ import CreateGroupForm from './components/CreateGroupForm';
 
 function init() {
   const shadowHost = document.querySelector('#create-group-form')!;
-  const shadowRoot = shadowHost.attachShadow({ mode: 'closed' });
+  const shadowRoot = shadowHost.attachShadow({ mode: 'open' });
   render(<CreateGroupForm />, shadowRoot);
 }