A violent quartet of criminals used fists, feet and a metal pot to pummel a disabled woman — then robbed her of her cash and her walker in a wild caught-on-video Harlem street attack. The 61-year-old victim told the Daily News Thursday she doesn’t know why the three women and a man set upon her shortly after 8 p.m. Tuesday, not far from her home... ...A young man in a white T-shirt and red shorts leaned against the scaffolding and coolly observed the fracas, doing nothing to intervene... “As they put me in the ambulance, he said, ‘You better watch...