## Summary
A cleanup pass across the blog: route and feed bugs fixed, SEO basics added, smaller and lazier images, accessibility fixes, and a real README. No content or design changes beyond small fixes.
## Bug fixes
- **Tag/category pages**: static params now use slugs, so pre-rendered pages match the links (before, `/tags/standard-model` was only rendered on demand and the pre-built pages said "Tag not found"). Unknown slugs now return a real 404, and there's a new not-found page.
- **Recently updated**: sorts by last modification *before* taking the top 5, so older posts that were updated recently now show up.
- **Atom feed**: `rel="self"` now points to `/feed.xml` (was `/feed`); `<updated>` uses the `updated` frontmatter field.
- **No-JS flash**: the `no-js` → `js` class swap runs in an inline `<head>` script before first paint, not after hydration.
- **Markdown links**: only internal paths go through `next/link`; `#anchors`, `mailto:` and links without an `href` no longer break.
- **Invalid HTML**: images in a paragraph together with text (e.g. "**Screenshots:**" followed by images on the Projects page) produced `<p><figure>` and a hydration error. Those paragraphs are now split.
- **Dates**: frontmatter dates are normalized to ISO, so `<time datetime>` values are valid. Formatting is pinned to Europe/Prague so a UTC build server can't shift a date by a day.
## SEO
- `sitemap.xml` and `robots.txt`
- Canonical URLs, Twitter cards and a feed link on every page, built by a shared `pageMetadata()` helper
- Generated Open Graph images: a site card, and for each post its cover image or a branded title card (pre-rendered at build time)
- `BlogPosting` JSON-LD on post pages
## Performance
- Only the post cover and the latest-post image are preloaded (was: every image)
- In-post image quality 100 → 90, plus responsive `sizes`
- Screenshots downscaled to 1800px wide; `linkboard-old.png` converted to WebP (3.1 MB → 60 KB)
- `CodeWrapper` is now a server component; only the copy button ships to the client
- Mermaid CDN script pinned to `11.17.2` for reproducible builds
## Accessibility
- Accessible names for icon-only links (share, social, mobile nav) and `aria-current` on active nav items
- Copy button: uses React state instead of mutating `innerHTML`, handles clipboard errors, announces the result to screen readers, and is no longer inside an `aria-hidden` header
- Code-block line numbers hidden from screen readers
- Image captions: the Markdown `"title"` becomes the caption; captions that only repeat the alt text are hidden from screen readers
## Content & maintenance
- **Frontmatter validation**: a missing or malformed field fails the build and names the file, instead of rendering a broken post
- **`draft: true` support**: drafts only render in development
- About/Projects/Setup pages share one `MarkdownPage` component; tag/category lists share `PostList`
- Markdown rendering is cached, so metadata and page share one render
- New README covering features, env vars, frontmatter schema, Markdown extensions and deployment
- Removed unused ESLint setup and the unrelated `hast` package; `oxlint`, `oxfmt` and `puppeteer` moved to devDependencies (locked versions unchanged)
- Typo fix in the Tessera cover alt text; removed unused `math`/`mermaid` flags from two posts
## Deployment notes
- **`SITE_URL` is now required**: the build fails with a clear error if it's missing.
- **Puppeteer is a devDependency now**: Nixpacks installs dev dependencies for the build by default, but check that Mermaid diagrams render on the first deploy (the Standard Model post has one).
## Testing
- `tsc --noEmit` and `bun run lint` pass
- `bun run build` passes; all 81 pages are generated statically
- Smoke-tested `next start`: posts, tags, categories, feed, sitemap and OG images return 200; unknown tags and routes return 404
- No block elements nested inside `<p>` in any built page
Reviewed-on: #1
