How to Use Intl.DurationFormat

Use `Intl.DurationFormat` when your app needs labels like `1 hr, 4 min`, `1:04:09`, or localized equivalents. Keep the duration math in your code, pass a plain duration object to `new Intl.DurationFormat(locale, options).format(duration)`, and stop maintaining English-only string helpers for timers, dashboards, media lengths, and elapsed-time UI....