A 28-year-old male from Delhi presents to the psychiatry outpatient department with a 6-month history of hearing voices that comment on his actions and occasionally argue with each other. He reports that these voices are "real" and originate from outside his head. He also believes that his neighbours are conspiring against him and have planted a device in his room to monitor his thoughts. His family reports a gradual decline in his academic performance and social withdrawal over the past year. He denies any substance use or head injury. Mental status examination reveals intact orientation but poor insight. What is the most likely diagnosis?