A 32-year-old woman from Delhi presents to the emergency department with acute onset fever (39.2°C), severe headache, neck stiffness, and photophobia for 6 hours. On examination, Kernig's sign and Brudzinski's sign are positive. A lumbar puncture is performed and cerebrospinal fluid (CSF) is sent for Gram stain and culture. The Gram stain shows gram-negative diplococci with a characteristic kidney bean or coffee bean morphology, located intracellularly within polymorphonuclear leukocytes. What is the most likely causative organism?