A 28-year-old woman from Delhi presents with a 6-month history of bloody diarrhea (8–10 stools/day), left lower abdominal pain, and tenesmus. She has lost 4 kg. On examination, she is afebrile, BP 110/70 mmHg, and has mild left lower quadrant tenderness. Colonoscopy reveals continuous mucosal inflammation, friability, and ulceration limited to the colon, with rectal involvement. Biopsy shows crypt distortion and crypt abscess formation. What is the most likely diagnosis?