The standoff between environmental protesters and German authorities at the Tesla car plant near Berlin deepened on Saturday, with both sides refusing to back down in the dispute over the giant site’s expansion. Activists at a forest camp organized to protest the US electric carmaker’s plans said they will take legal action to prevent authorities from forcing them to dismantle tree houses they built and leave. Protesters will “exhaust all legal means to prevent an eviction,” according to a statement from the “Stop Tesla” initiative. The group has not said what specific steps it intends to take…