SITUATION EXPLAINED: Elon Musk just backed a $3.5 trillion merger of SpaceX and Tesla, which would be the biggest deal in history. • Musk backed it on an investor call, but he’s conflicted and has to stay out of the talks, so insiders worry it’ll draw shareholder scrutiny and add weeks of delay • Independent committees at both companies are weighing SpaceX buying Tesla or a new holding company, likely in an all-stock deal • It echoes Tesla’s 2016 SolarCity buyout, where Musk was also on both…