feat: enhance accessibility and testing with data-test attributes and improve error handling

apps/web/app/[locale]/home/[account]/courses/[courseId]/attendance/page.tsx

@@ -6,6 +6,7 @@ import { getSupabaseServerClient } from '@kit/supabase/server-client';
 import { Badge } from '@kit/ui/badge';
 import { Card, CardContent, CardHeader, CardTitle } from '@kit/ui/card';
 
+import { AccountNotFound } from '~/components/account-not-found';
 import { CmsPageShell } from '~/components/cms-page-shell';
 import { EmptyState } from '~/components/empty-state';
 
@@ -29,7 +30,7 @@ export default async function AttendancePage({
     api.getParticipants(courseId),
   ]);
 
-  if (!course) return <div>Kurs nicht gefunden</div>;
+  if (!course) return <AccountNotFound />;
 
   const selectedSessionId =
     (search.session as string) ??