Fix favicon: apply the new red RubyUI mark (#476)

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