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