A 28-year-old woman from Delhi presents with a 3-month history of arthralgia affecting her hands, wrists, and knees, along with a malar rash that worsens in sunlight. She reports fatigue, low-grade fever, and recent hair loss. On examination, she has a butterfly rash over the cheeks and nasal bridge, oral ulcers, and non-erosive arthritis. Laboratory investigations show: ANA positive (1:640, homogeneous pattern), anti-dsDNA antibodies positive (180 IU/mL; normal <70), anti-Smith antibodies positive, complement C3 level 45 mg/dL (normal 80–160), and urinalysis shows mild proteinuria (0.8 g/24 h) with occasional RBC casts. Which of the following is the most appropriate next step in management?