CULIACÁN, Mexico—A man’s body, hands bound and covered by a blue tarp, lies by the side of the road where it had been dumped minutes earlier. A blood-soaked sign says he was a “Chapito,” a member of one of two criminal factions fighting for control of this city, the cradle of Mexico’s transnational narcotics industry.  Such macabre finds are common in Culiacán—a city of luxury car dealerships, fancy malls, and makeshift fentanyl labs—marking the shifting lines of nearly two years of relentless civil war between the two main clans of the pioneering Sinaloa cartel. It’s a war that the Chapitos,…