How the songwriter turns disorientation into irresistible, strangely comforting music — “Black Bathing Suit,” from Lana Del Rey’s latest record Blue Banisters, has always bewitched and perplexed me — not unlike Lana herself, who captivates me with her sound but so often eludes my grasp. The song opens with seagulls squawking over a delicate piano as it slowly plays in 4/4…