A 28-year-old man presents with a 3-day history of productive cough with yellow sputum, fever (38.5°C), and shortness of breath. On examination, his respiratory rate is 24/min, heart rate is 110/min, BP is 115/70 mmHg, and oxygen saturation is 95% on room air. Auscultation reveals crackles in the right lower lobe. His CURB-65 score is 0. What is the most appropriate antibiotic choice according to NICE guidance for community-acquired pneumonia (CAP)?