A 28-year-old woman with a history of childhood asthma presents with episodic wheeze and chest tightness triggered by viral infections and exercise. Her lung function is normal between episodes, and she currently uses salbutamol as needed about twice per week. She has had one mild exacerbation in the past year requiring a short course of oral steroids. According to the 2021 Canadian Thoracic Society asthma guideline, which controller strategy is preferred for mild asthma in adults?