Fix duplicated cookie-file arg in Task 7's verification curl command

docs/superpowers/plans/2026-08-29-admin-account-management.md

@@ -1630,7 +1630,7 @@ curl -sS -c /tmp/plan-cookie-cp.txt -b /tmp/plan-cookie-cp.txt -o /dev/null \
   -X POST http://localhost:8092/admin/login -d "username=changepasstestuser&password=oldpass123"
 
 echo "wrong current password -> expect error shown, no change:"
-curl -sS -b /tmp/plan-cookie-cp.txt /tmp/plan-cookie-cp.txt http://localhost:8092/admin/account/password \
+curl -sS -b /tmp/plan-cookie-cp.txt http://localhost:8092/admin/account/password \
   -X POST -d "currentPassword=wrongcurrent&newPassword=newpass456" -o /tmp/cp-wrong-body.html
 grep -c "không đúng" /tmp/cp-wrong-body.html