Create a single self-contained HTML file that implements a simple Pomodoro Timer app. The app must: 1) Display a 25-minute countdown timer, 2) Have Start, Pause, and Reset buttons, 3) Show visual progress, 4) Play a sound or show a notification when time is up, 5) Work offline after download, 6) Use only HTML, CSS, and JavaScript (no external libraries), 7) Be responsive for mobile and desktop. Deliver one HTML file.