WASHINGTON — A colonial-clad Capitol rioter — dubbed “Conan O’Riot” because of his resemblance to former late night talk show host Conan O’Brien — pleaded guilty to a Jan. 6 charge on Tuesday.Derek Nelson, a 30-year-old former Marine, was arrested in Illinois in October 2023, more than two years after he was identified by online “sedition hunters” who have aided the FBI in cases against hundreds of defendants.Nelson pleaded guilty to a count of entering and remaining in a restricted building, which carries a maximum sentence of one year in prison. U.S. District Judge Carl J. Nichols…