With its white-columned neoclassical facade, the Ritz-Carlton, San Francisco, has been a stately—if slightly imposing—retreat in scenic Nob Hill since opening in 1991. But the hotel’s century-old skin, which formerly housed the West Coast headquarters of a life insurance company, belies fresh new interiors that reflect the modern momentum of the City by the Bay. Completed in March, the Ritz-Carlton’s three-year renovation has transformed each of the 336 rooms and suites into sleek urban escapes featuring state…