A 72-year-old previously healthy man comes to clinic because his wife noticed that his eyes are yellow. Recently he has found that his urine is dark and the stool light in color. He has recently had anorexia, but otherwise feeling well without other complaints. He smoked cigarettes for 30 years but quit 15 years ago. He is deeply jaundiced. There is a nontender smooth globular mass consistent with an enlarged gallbladder in the right upper quadrant of his abdomen. The rest of his examination is normal. Which of the following is the most likely diagnosis in this patient?