If no weapons are involved, next time I am facing a gang in a dark alley, I want Gabriel Manro on my side. Making his debut here, in the West Bay Opera’s sensational production of Verdi’s La Forza del Destino, Manro is a new kind of baritone: not lyric, not helden, not Kavalier, not Bariton-Martin — none of those. Rather, he’s a knock-down baritone.