A 32-year-old man from Delhi presents with a 3-month history of auditory hallucinations, paranoid delusions, and disorganized speech. He was started on risperidone 4 mg/day 2 weeks ago. Today he reports severe muscle rigidity, high fever (39.5°C), altered mental status, and profuse sweating. Laboratory investigations show CK 1200 U/L, creatinine 1.8 mg/dL (baseline 0.9), and WBC 12,500/μL. What is the most appropriate immediate management?