SAN DIEGO — Jon Lester agreed Tuesday night to a $155 million, six-year contract with the Cubs, the first big deal of the offseason involving a top-level starting pitcher and one Chicago hopes will help end more than a century of frustration at Wrigley Field's Friendly Confines. Lester's contract, agreed to on the second day of baseball's winter meetings, contains an option for 2021 that, if it becomes guaranteed, would make the deal worth $170 million over seven seasons. The average annual value of $25.8 million is the second-highest for a pitcher behind Clayton Kershaw's $30.7 million as part of a $215 million, seven-year deal with the Los Angeles Dodgers that began this year.