A 4-year-old boy from Delhi presents with intense itching and erythematous, lichenified plaques over the flexural surfaces of his elbows and knees for the past 18 months. His mother reports the rash worsens during winter and improves in summer. On examination, he has dry skin (xerosis), Dennie–Morgan folds, and an elevated serum IgE level of 850 IU/mL. He has a personal history of allergic rhinitis and a family history of asthma in his father. What is the most appropriate first-line topical agent for managing the acute flare in this patient?