chore: migrate site to grid.unece.org

This MR re-homes the GRID pilot identifiers and site URLs from the GitLab Pages namespace path https://un.opensource.unicc.org/unece/uncefact/gtr/ to the custom domain https://grid.unece.org/, following the Docusaurus url/baseUrl change that now serves the site from the root path (the same unique-domain approach agreed for all UNECE projects on GitLab, see spec-unvtd!65 (merged)).

The pilot did:web identifiers change with the move, because did:web encodes the hosting domain and path in the identifier itself: did:web:un.opensource.unicc.org:unece:uncefact:gtr:pilots:atlantis becomes did:web:grid.unece.org:pilots:atlantis. Once this is cut over, any credential issued using the old DIDs will no longer verify. Resolution of an old DID fails the did:web requirement that the resolved DID document's id match the DID being resolved, and a credential proof's verificationMethod embeds the full old DID, so key dereferencing fails with it. HTTP redirects cannot repair either, because the identifier is the string itself. If credentials have been issued against the old DIDs, new credentials will need to be created and signed using the new DIDs. Just note, the committed pilot DID documents carry placeholder public keys, so no working issuance is anchored to them within this repository.

Meeting minutes are left unchanged as historical records; the old links keep resolving via the GitLab redirect. The version-0.1 docs are retrofitted to the new domain. The internal registrar entries touched here will show a degraded trust badge until re-signed by an authorised allowed_signers key.