By Trevor Hunnicutt and Jeff Mason WASHINGTON (Reuters) -President Joe Biden on Thursday will unveil his administration’s first steps to curb gun violence, including a plan to reduce the proliferation of “ghost guns,” after a slew of mass shootings have put pressure on him to act. Biden will announce that the Justice Department intends to issue a proposed rule within 30 days to help reduce the increasing prevalence of untraceable, self-assembled “ghost guns,” a White House official told reporters. The details of the rule were not immediately clear. The department also will issue proposed rules…