Kim Kardashian is officially on lockdown ... again -- Kanye West pulled off a huge birthday surprise by renting out an entire baseball stadium and asking Kim to marry him Monday evening. Naturally, Kanye went super-baller for the proposal -- sources connected to the couple tell us Yeezy flew Kim to San Francisco, blindfolded her, and whisked her off to AT&T Park ... home of the Giants and popped the question with a 15 carat Diamond Ring!!!