Close the next ended GL period if it is ready

Re-checks readiness for the period named by periodId, or else the earliest ended open period. Only when it is ready does it post every due schedule entry, generate the closing entry, mark the period closed and update the books status. A close that cannot proceed (not ready, already closed, a failed schedule posting, failed clearing verification, or a closing entry that cannot be generated) answers 200 with closed: false and a reason. Requires company role admin or owner, the same authority as POST /companies/{companyId}/gl-periods/{id}/close; API keys are refused with 403 (#2411).