A nyone who’s seen Julia Cumming perform knows she’s a star. As the lead singer and bassist of the New York rock band Sunflower Bean , she has spent more than a decade commanding stages with confidence, her vocals ringing out loud and clear across the din of countless clubs and theaters. But for most of that time, if you tried suggesting that she go solo, she was adamantly opposed. “My response would be, ‘Fuck you,’” says Cumming, 30. “It would piss me off.” That advice, which she heard often