A 24-year-old man, who was two weeks away from moving out of his East New York housing projects, was gunned down in front of his home yesterday. Robert Castro was fatally shot just after midnight Saturday at East New York's Boulevard Houses with no clear motive and no arrests yet made. Castro was preparing to marry his long-term girlfriend and mother of his two young children. A recently laid off janitor with a previous record for drug and weapon possession was called "the greatest father ever" by Shamica Mercato, his girlfriend of ten years.