Fix favicon: apply the new red RubyUI mark

The red brand update to the favicon never reached main (a previous PR merged with the black version before the red change went in). This applies the final red mark (#b32328) on a 90% white rounded tile to the full icon set in docs/public/: icon.svg, favicon.ico, favicon-16x16, favicon-32x32, apple-touch-icon, android-chrome-192/512, icon.png.

Author: Sergio-Linkana