SANTA CLARA - You'll have to pardon 49ers cornerback Tarell Brown if he seemed a bit distracted during Thursday's practice. He had a good excuse.Cornerback Nnamdi Asomugha, above, signed to a one-year deal by the 49ers in the offseason, stretches out on the first day of training camp in Santa Clara. At right, 49ers coach Jim Harbaugh puts it to wide receiver Ricardo Lockette at practice. Story, Page C6Marcio Jose Sanchez Associated Press