docs: 2-column registry layout with descriptions (#498)

* fix: strip XML declarations and Inkscape metadata from SVG icons

Some registry icons (e.g. Corust Agent) contain XML declarations,
Inkscape namespaces, and sodipodi elements that break JSX/MDX parsing.

* docs: use 2-column layout with descriptions for registry agents

Switch from 3-column grid to 2 columns and include agent descriptions
in the cards for better readability.

Author: ignatov