A 28-year-old man from Delhi presents with a painless ulcer on the glans penis for 3 weeks. On examination, the ulcer has a well-demarcated border, indurated edges, and a clean base with scanty serous discharge. Regional lymph nodes are enlarged, firm, and non-tender. Dark-field microscopy of the ulcer exudate shows motile spirochetes. The patient denies systemic symptoms. What is the most likely stage of syphilis?