- Replace the create-next-app README with real project docs (features,
env vars, frontmatter schema, Markdown extensions, deployment)
- Drop ESLint (unused by any script; oxlint is the linter) and the
unrelated 'hast' package; move oxlint, oxfmt and puppeteer to
devDependencies (locked versions unchanged)
- Extract PostList, used by the tag and category pages
- Use shared Intl formatters for post dates, pinned to Europe/Prague so
the build server's timezone can't shift dates
- Use <h1> for the tag/category page headings (same styling)
- Remove math/mermaid flags from posts that don't use them; fix a typo
in the Tessera cover alt text
