D018: Multi-page site + persistent header nav

Context: A UX audit (and Saif's own reaction) found the single-page structure (~11,000px scroll) had no navigation, you could only scroll or "back to top," couldn't jump to Work/Brain/Analytics from the top.

Decision: Convert to a multi-page site with a persistent, responsive header nav: Home · Work · About · Brain · Analytics · Contact (+ the existing language pill + theme toggle). Home becomes a concise landing (hero + highlights + teasers), not the whole story. Add subtle page transitions (Astro view transitions), reduced-motion-safe.

Why: Discoverability + a sense of a real product. Supersedes the original single-page IA, the felt experience beat the plan (D001 - Site as Proof Principle).

Supersedes: the single-page narrative in the original §2 IA. Case studies keep /work/[slug]; About / How-I-work / Contact get real pages.