part-time work Korea international students D-2 part-time job d-10 visa korea student visa korea attendance rules international student Korea student visa korea rules international student korea immigration attendance korea student visa korea attendance work rules international student korea immigration D-2 visa Korea international student attendance Korea Korean university visa student visa instability Korea international student administrative risk Korea international student visa korea problems student visa pattern issues Korea student attendance Korea international student immigration review Korea student visa Korea job seeking visa korea study in Korea hikorea d10 student visa document mistake Korea international student visa rejection Korea student part time work korea visa international student job rules korea student visa after graduation student visa attendance rules Korea university change immigration Korea student work permit Korea part-time work Korea D-4 work permission student visa transfer Korea