Eduard Sagyndykov owns the Minsk apartment where Lee Harvey Oswald once lived.Credit...Andrei Liankevich for The New York Times MINSK, Belarus — At the end of the cold war, the leadership of the K.G.B., demoralized and seeking favor with the pro-Western reformers then coming to power in post-Soviet states, briefly opened its files on the accused assassin of John F. Kennedy, Lee Harvey Oswald. The