Create a realistic K-pop fan birthday billboard ad in a clean Seoul subway station, 16:9. Large digital billboard on the wall is the focus. The billboard celebrates fictional member '서윤' with elegant pastel graphics, soft sparkles, and readable Korean message: '서윤, 너의 모든 순간을 응원해', '루미나', '2026.05.08'. Subway corridor, people motion blur, billboard glow reflecting on floor. Premium fan event mood, no real idol, no brand logos, no watermark.