A 67-year-old retired teacher presents with a 9-month history of insidious onset symptoms. He has noticed increasing difficulty with fine motor tasks like fastening buttons, his handwriting has become smaller, and he walks with slower, shorter steps. His wife notes he has developed a tremor in his right hand, most noticeable when he is resting. On examination, you observe facial hypomimia, a resting pill-rolling tremor of the right hand, cogwheel rigidity in the upper limbs (worse on the right), and bradykinesia. What is the most likely diagnosis?