A 35-year-old previously healthy non-pregnant woman presents with 3 days of fever, productive cough with rusty sputum, and pleuritic chest pain. She is haemodynamically stable with normal oxygen saturation and CURB-65 score of 0. Chest radiograph confirms right lower lobe community-acquired pneumonia. According to Canadian outpatient CAP recommendations, what is the most appropriate first-line antibiotic?