Authorities said they apprehended Ahmad Khan Rahami, the 28-year-old wanted in connection with weekend bombings in Manhattan and Seaside Park, N.J., after a shootout Monday with police officers. The bloody incident capped off a frantic few days in this region and beyond, marked by the dual bombings, a stabbing spree in Minnesota and then, Sunday night, the discovery of still more explosive devices at a train station here. Even as the widening probe into the bombings continued across this region, authorities sought to reassure residents that the the bombings and additional explosives appeared to be the work of a lone person rather than a larger network.