Add option to require Both Account and Contact on CRM Events

Today, CRM events can be saved with either an Account or a Contact associated, but not necessarily both. Add a configurable option (organization or admin-level setting) that allows administrators to require both an Account and a Contact before an event can be saved.

This should be configurable rather than mandatory for all customers, allowing organizations to enable the requirement based on their business processes.

Acceptance Criteria

• Admin setting to require both Account and Contact on Events.

• Validation prevents saving when either field is missing.

• Clear user messaging identifying which required field is incomplete.

• Existing organizations that do not enable the setting experience no change in behavior.