By Joseph Campbell and Alessandra Prentice ZAPORIZHZHIA, Ukraine (Reuters) – Russia unleashed rockets on Tuesday on an encircled steel works in Mariupol, Ukraine’s last redoubt in the port city, after a ceasefire broke down with some civilians still trapped beneath the sprawling site despite a U.N.-brokered evacuation. Scores of evacuees who did manage to leave under United Nations and Red Cross auspices over the weekend after cowering for weeks under the Azovstal plant reached the relative safety of Ukraine-controlled Zaporizhzhia. More than 200 civilians remain in the plant, according to Mar…