Closes a goal, moving it to the closed status. An optional comment may be included in the request body to record a note at closing time. Returns the updated goal object. Validate the result using the returned status, percentComplete, and completionDate fields; do not rely solely on lastChangedDateTime as the confirmation timestamp, because it may not match the HTTP response time or may reflect BambooHR's internal timezone/update semantics. Note: Cascading goals with visible children cannot be closed.