He was the nerdy tech titan who impacted everyone’s daily life, but no one knew who he was. Yet Google cofounder Sergey Brin has suddenly burst on to the scene and transformed into a political powerhouse — and many think it’s due to his girlfriend. Despite his escalating war with Sacramento — mainly over the state’s crippling billionaire tax — little is known about the billionaire’s private life. Brin has quietly traded Silicon Valley’s liberal bubble for a far different backdrop — a sprawling