A 32-year-old man from Mumbai presents with a 3-year history of recurrent abdominal pain, non-bloody diarrhoea, and weight loss of 8 kg. On colonoscopy, patchy areas of mucosal inflammation alternating with normal-appearing segments are seen throughout the colon and terminal ileum. Biopsy from an inflamed area shows transmural inflammation with non-caseating granulomas in the lamina propria and submucosa. The patient also has a history of perianal skin tags and a draining fistula. What is the most likely diagnosis?