feat: hide certificate buttons for non-team members

- Added isTeamMember check (session user ID === certificate user ID)
- Hide all action buttons (Download, Print, View Submission) for non-members
- Hide "Back to Submission" button in header for non-members
- Unauthenticated users and other users can view certificate but cannot interact with buttons

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/hackathon/src/app/certificate/[certId]/page.tsx

@@ -4,6 +4,7 @@ import { Button } from '@imphnen-frontend-service/ui/atoms';
 import { decodeCertificateId } from '../../../utils/certificate';
 import {
   useCertificatePublicData,
+  useAuthStore,
 } from '@imphnen-frontend-service/service';
 import QRCode from 'qrcode';
 import html2canvas from 'html2canvas';
@@ -17,6 +18,7 @@ interface DecodedCert {
 const CertificatePage: FC = (): ReactElement => {
   const { certId } = useParams<{ certId: string }>();
   const navigate = useNavigate();
+  const { session } = useAuthStore();
   const [decodedInfo, setDecodedInfo] = useState<DecodedCert | null>(null);
   const [error, setError] = useState<string | null>(null);
   const teamNameRef = useRef<HTMLHeadingElement>(null);
@@ -74,6 +76,9 @@ const CertificatePage: FC = (): ReactElement => {
   // Certificate name from the user data
   const certificateName = certificateUser?.fullname;
 
+  // Check if current user is viewing their own certificate (team member)
+  const isTeamMember = session?.user?.id === decodedInfo?.userId;
+
   // Dynamic font sizing: shrink by 2px if height exceeds 80px
   useEffect(() => {
     const adjustFontSize = (
@@ -281,7 +286,7 @@ const CertificatePage: FC = (): ReactElement => {
                 {team?.name}
               </p>
             </div>
-            {team && (
+            {team && isTeamMember && (
               <Button
                 variant="secondary"
                 onClick={() =>
@@ -472,6 +477,7 @@ const CertificatePage: FC = (): ReactElement => {
           )}
 
           {/* Actions */}
+          {isTeamMember && (
             <div className="bg-gray-50 dark:bg-gray-800 p-6 grid grid-cols-2 xl:grid-cols-3 gap-3 justify-center no-print">
               <Button
                 variant="secondary"
@@ -501,6 +507,7 @@ const CertificatePage: FC = (): ReactElement => {
                 </Button>
               )}
             </div>
+          )}
         </div>
 
         {/* Info Box */}