The country world feigned surprise when, after three albums of Music Row-indebted songcraft, Taylor Swift formally embraced pop on 2012’s Red. But no one should have been shocked: Any 14-year-old capable of persuading her parents to move from suburban Pennsylvania to Nashville for her career clearly has the ambition to burn. And the thrill of following Swift’s rise has been watching her execute it flawlessly, largely because her melodic intelligence is equal to that ambition.