Hide-on-Scroll Header

Build a "Hide-on-Scroll Header" React component.

CONCEPT: An article page header that respects reading: it hides on downward scroll, reappears on upward scroll, compacts after 80px, and draws a cobalt progress bar along its bottom edge.

LAYOUT & CONTENT:
- Header: wordmark, section name in mono, and a 'Subscribe' pill. Paper background, bottom 1px rule.
- Body: an article with a headline and several paragraphs for scrolling.

INTERACTIONS & MOTION:
- useScroll on the page (or a scroll container) and useMotionValueEvent(scrollY, 'change') to compare with previous value; set hidden when delta > 0 and y > 80.
- Animate header y: hidden ? '-100%' : 0 with spring stiffness 400 damping 40.
- Progress bar scaleX = scrollYProgress smoothed by useSpring stiffness 200 damping 30, origin-left.

DESIGN SYSTEM (non-negotiable):
- Palette: paper background #FAF9F6, deep charcoal #121212 for text and 1px borders, ONE warm accent: cobalt #1D4ED8 or terracotta #D9534F. Secondary surface #F2EFE8.
- Typography: Swiss / editorial. A tight grotesk for UI (Instrument Sans, Inter Tight or similar) with negative tracking on display sizes; an italic serif (Instrument Serif) used sparingly for one emphasized word.
- NO dark-mode neon, NO glow, NO glassmorphism, NO backdrop blur, NO purple-to-blue gradients, NO emoji icons. Solid fills, hairline rules, honest shadows (hard offset or none).
- Motion: Framer Motion with spring physics (type: "spring", stiffness 300-500, damping 20-35). Animate transform and opacity only. Respect prefers-reduced-motion via useReducedMotion().
- Icons: lucide-react, 1.5px stroke.
- Accessibility: real <button>/<a>/<label> elements, visible focus ring (2px cobalt, 3px offset), keyboard operable, aria attributes where state changes.

OUTPUT: one self-contained React component file (Tailwind CSS v4 utility classes, framer-motion, lucide-react), no external images, default export, ready to paste into a Next.js App Router page with "use client".