One wears an impeccably tailored navy blue suit. The other sports a giraffe-print dashiki shirt. Meet the renewable-energy odd couple, the environmental activist and his onetime target, the chief of Italy’s largest utility. A year ago, Kumi Naidoo, the head of Greenpeace International, and Francesco Starace were sworn enemies, after the group said Enel SpA’s coal plants were killing people. Now, they’re drinking orange juice together at the Four Seasons in New York, discussing the…