A 28-year-old woman, 6 weeks pregnant, from endemic Jharkhand presents with a 3-day history of fever (38.8°C), myalgia, and vomiting. Thick blood smear shows *Plasmodium vivax* with 0.5% parasitemia. She is haemodynamically stable, alert, with no jaundice or neurological signs. What is the most appropriate antimalarial regimen?