A 27-year-old female presents with progressive fatigue, palp…

A 27-year-old female presents with progressive fatigue, palpitations, and generalized weakness. On physical examination, she has pale conjunctiva and nail beds, tachycardia, a soft systolic flow murmur, angular cheilitis, stomatitis, glossitis, and spoon-shaped nails (koilonychia). Which of the following is the most likely diagnosis?