Correct specialty on a group-location-network specialty record

Replaces the specialty identifier on a practitioner specialty association at the group-location-network level. This is a data-correction operation — it does not trigger termination events, lifecycle changes, or downstream workflow notifications. Use it when the wrong specialty was linked at this level and the record needs correcting in place without triggering a termination cycle; for corrections at the group-location level without a network, use PATCH /practitioners/group-practitioner-location-specialties/specialty instead. The specialty association record must already exist, and the replacement specialty must be a valid, active tenant specialty.