A former Chelsea High honors student who came from Guatemala at age 12 is pleading to stay in the United States as federal authorities try to deport him and a Bay State congressman and local officials rally at his side. “I have so many dreams, and this is the country where I want them to come true,” said Mario Rodas, 19. “I feel really upset. They could send me to a country away from my family and friends. It’s devastating.” The case has put the thin, bookish young man with a passion for politics in the middle of a fierce...