By Mitchell Forde It’s been less than 24 hours since the San Francisco 49ers and Carolina Panthers shook up the NFL landscape with a blockbuster deal. Running back Christian McCaffrey is now a 49er. Friday morning, McCaffrey arrived in San Francisco and offered a message for 49er fans on social media. “Touched down in The Bay! Feels good to be back! Bang Bang Niner GangGod is Good” — Christian McCaffrey McCaffrey’s tweet comes a few hours after he posted a heartfelt goodbye message to Carolina Panthers fans. McCaffrey referenced being back in the Bay Area. He played his college football at St…