User Story
As a user,
I want to be prevented from creating a new case for an account with an open case,
so that cases can be resolved sequentially and avoid duplication of effort.
Acceptance Criteria:
- The system checks for any open cases linked to the account before allowing new case creation.
- If an open case exists, the system displays a message: "A case is already open for this account. Please resolve it before creating a new case."
- If no open case exists, the user can proceed with case creation.