Replace the hand-crafted HTML website with a Next.js App Router project
using `output: "export"` for GitHub Pages compatibility.

Key improvements:
- Eliminate duplicated CSS, navigation, footer, and analytics across pages
- Shared components: Footer, BlogHeader, Analytics, Icons, Lightbox, ShareButton
- Blog posts rendered at build time via marked (previously client-side)
- Proper SEO: per-page metadata via Next.js Metadata API
- Clean URLs: /blog/[slug] instead of post.html?slug=
- Gallery lightbox converted from CSS :target to React state
- Blog content moved to content/ for clean separation
- Images moved to public/ as standard Next.js convention
- GitHub Actions workflow updated to build Next.js before deploying
- Workflow scoped to only trigger on website/** changes

https://claude.ai/code/session_01RCSNNgGLcnSwXTqws2cfgq