Minimal post (test fixture)

Minimal test fixture used by $slug.test.tsx. No headings, no tags — covers the
null branches of TOC rendering and tag-list rendering in routes/posts/$slug.tsx.

Slugs prefixed with _ are excluded from /posts listing (production publishing
surface) but remain reachable via direct getRenderedPost(slug, lang) (the
virtual:rendered-posts lookup that backs /posts/$slug) so test fixtures can
be SSR'd without polluting the index.