/scroll-fx — Scroll Effects

Add scroll-based effects:

Reveal on scroll: Elements fade in and translate up 20-30px as they enter the viewport.

• Use IntersectionObserver with threshold: 0.1
• Stagger siblings with 80-120ms delays
• One-shot (don't re-hide on scroll up)

Parallax: Background layers move at different rates.

• Use CSS scroll-driven animations where supported
• Fall back to transform: translateY with scroll listeners
• Keep subtle (0.1-0.3 rate difference)

Always respect prefers-reduced-motion.