After months of touring South Florida’s most fortified islands and branded penthouses, the final stop on the “billionaire bunker” circuit reveals a shift in the ultra-high-net-worth psyche. Wealthy transplants are no longer just buying security – they are buying history. Tucked behind the lush, designer landscaping of a Gothic-modern $18 million estate, the “Silicon Grove” era has arrived. Here, the bunker isn’t a modern glass box, but instead f…