PARIS — France identified a 27-year-old Belgian who once boasted about killing “infidels” and fought for the Islamic State group in Syria as the mastermind of the Paris attacks, and President Francois Hollande vowed Monday to forge a united coalition capable of defeating the jihadists at home and abroad. Addressing lawmakers after France observed a minute of silence honoring the 129 people killed and 350 wounded, Hollande said the victims came from at least 19 nations, and the international community, led by the United States and Russia, must overcome their deep-seated divisions over Syria to destroy the Islamic State on its home turf. “Friday’s acts of war were decided and planned in Syria.