A 32-year-old man from Bangalore presents with his sister, who reports a 5-day period during which he felt unusually happy, was more talkative than usual, and started a new hobby (photography) with intense enthusiasm. He slept only 4–5 hours per night but did not feel tired. He made some impulsive purchases but did not lose his job or face serious consequences. He denies any psychotic symptoms. Three years ago, he had a 2-month depressive episode treated with sertraline. He has no history of hospitalization for mood episodes. What is the most likely diagnosis?