A 45-year-old man presents with a 5-day history of fever, productive cough with purulent sputum and left-sided pleuritic chest pain. He has no significant comorbidities and is stable with temperature 38.2 °C, BP 120/70 mmHg, HR 92 bpm, SpO2 95% on room air. Chest X-ray shows a left lower lobe consolidation. You assess this as low-severity community-acquired pneumonia suitable for outpatient management. According to Therapeutic Guidelines, which empirical oral antibiotic is most appropriate first-line?