fix(seo): embeds de conjuntos exibem nomes dos conjuntos, e não uma frase genérica - #1658

next/head only deduplicates <meta> on name/httpEquiv/charSet/itemProp —
`property` is not on that list — so the og:* tags in _app.js and the ones
in each page were both emitted. _app.js rendered first and crawlers take
the first occurrence, so every shared URL showed the generic site card
instead of the page's own title, description and image.
- key the defaults in _app.js (ogtitle, ogdesc, ogimage, ogurl, ogtype,
 ogsitename, imagesrc) so page-level tags replace them instead of
 appending; next/head keeps the last element for a given key
- drop twitter:title/description/image/url from _app.js and keep only
 twitter:card: crawlers fall back to the og:* tags, so each page's
 Twitter card now matches the og card it already defines
- og:url is the current path instead of always the site root, and the
 dataset page emits <link rel="canonical"> without the ?table= param
- key og:type/og:url in blog/[slug] and docs/[slug], which were also
 being overridden by the defaults (og:type read "website", not "article")
- strip markdown and truncate dataset descriptions at a word boundary
 via formatMetaDescription in utils.js
Dataset pages now preview with their own name in the domain's language
(pt/en/es), verified against the production backend on all three locales.