A 72-year-old woman with a history of hypertension and osteoarthritis presents with a 3-day history of increasing shortness of breath, cough productive of green sputum, and fever. Her respiratory rate is 24/min, oxygen saturation is 93% on air, heart rate is 105 bpm, blood pressure is 140/85 mmHg, and temperature is 38.1°C. Chest auscultation reveals crackles in the right lower lobe. Her CURB-65 score is calculated as 1 (Age ≥65). According to NICE guidelines, what is the most appropriate initial management setting?