A 28-year-old male construction worker is brought to the emergency department 45 minutes after a fall from scaffolding (3 metres). On arrival, he is drowsy but arousable to verbal commands. He opens his eyes to pain, obeys commands inconsistently, and speaks in confused sentences. His pupils are equal and reactive. CT head shows a 12 mm acute subdural haematoma without midline shift. Blood pressure is 128/82 mmHg, heart rate 92/min, respiratory rate 18/min. What is his Glasgow Coma Scale (GCS) score, and what is the most appropriate immediate management?