docs: GitHub social banner in the site's /node visual language

Generated from lofi's brand tokens and the /node landing furniture:
Grenze Gotisch mark, the playground scene rendered still, and the JSR
install command. Kept in lockstep with lofi's copy at
docs/assets/brand/ in that repo.

commit

1f83f723ce3cac025800407806aa5c4f51bc8a23

parent

a9544ff57ae6c4d412ae283c074e7dde9a8ac0ad

author

Dami <dami.etoile@gmail.com>