fix: handle undefined updatedAt in profile page

Add null check for user.updatedAt before passing to formatDate function.
The User type defines updatedAt as optional (string | undefined), so we
need to handle the undefined case to prevent TypeScript compilation errors.

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

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

app/profil/page.tsx

@@ -228,7 +228,7 @@ export default function ProfilePage() {
                   Dernière modification
                 </label>
                 <p className="text-sm text-gray-900 mt-1">
-                  {formatDate(user.updatedAt)}
+                  {user.updatedAt ? formatDate(user.updatedAt) : 'N/A'}
                 </p>
               </div>
             </CardContent>