GSAP ScrollTrigger: ステップハイライト付きインタラクティブタイムラインプログレスバー

Create an interactive timeline progress bar using GSAP ScrollTrigger that reacts to scroll position. Include 5 milestone steps, each revealing content with staggered animations on scroll. Use a fixed progress bar with step markers that highlight as user scrolls through sections. Add smooth appearance animations for step content using GSAP from and to tweens. Ensure mobile responsive with touch support.