A 28-year-old man from Delhi presents with purulent urethral discharge and dysuria for 3 days. He reports unprotected sexual contact with a new partner 5 days ago. On examination, there is a thick, yellowish-green urethral discharge. Gram stain of the urethral smear shows gram-negative intracellular diplococci within polymorphonuclear leukocytes. What is the most likely diagnosis and the preferred initial antibiotic regimen?