First the flood, now the mold — and for many San Jose residents the coughing and sneezing has already begun. More than a week after Joan Rivas-Cosby fled her Olinder neighborhood home with her cats Persimmon and Friday in tow, the ceiling of her basement — where standing water festered for days — turned into a petri dish, dotted with tiny light blue and green fuzzy spores growing on practically every panel. “It’s heart-wrenching,’’ said the twice-widowed mother of two grown children. “Nothing is the same anymore. Everything for me has changed overnight.’’