German metalworkers’ union IG Metall on Thursday said it is prepared to negotiate with Volkswagen, including on the introduction of a four-day week, after the auto giant announced cost-cutting plans that could threaten thousands of jobs. “We should leave no stone unturned when it comes to ideas on how we can maintain jobs and locations,” the head of the powerful union, Christiane Benner, said in the northern city of Hanover. Benner said plant closures and redundancies, which Volkswagen said on Monday it could no longer rule out at its core VW brand, are “absolute red lines” for the union. IG M…