A 32-year-old woman presents with sudden onset sharp right-sided pleuritic chest pain and dyspnoea following a vigorous coughing bout. She is tall and slim, with no past medical history. On examination, she is mildly tachypnoeic with reduced breath sounds and hyper-resonance over the right apex. Observations are stable: respiratory rate 22, pulse 90, oxygen saturation 97% on air. Chest X-ray confirms a 3 cm right primary spontaneous pneumothorax. What is the most appropriate initial management?