MIAMI — The sense of dread proved all too real Tuesday, with the Miami Heat announcing that guard Dru Smith sustained a season-ending torn left Achilles tendon in Monday night’s victory over the Brooklyn Nets. Having recently emerged as a prime rotation component in his comeback from his season-ending knee injury a year ago, Smith was helped off the court with 8:18 left in Monday night’s second quarter, a collective shudder enveloping Kaseya Center. For his coach and teammates, this was more than a player on a two-way contract going down.