Recolor the logo, favicon, and research diagrams to burnt orange

Follows the CSS accent change. The nine research SVGs were a plain hex
swap. The logo and favicon are raster, so each was remapped rather than
hue-filtered.

logo3.png is two flat colors plus antialiasing, so every pixel was
projected onto the gold-to-gray axis, the gold endpoint swapped, and
the residual added back. That maps both endpoints exactly and preserves
all 539 blend shades without fringing.

favicon.ico carried its own duller gold (#a39259) and nine embedded
sizes. A saturation-gated remap leaves the neutral background and
lettering untouched. The container is rebuilt by hand so each size is
recolored in place, AND masks copied verbatim and payload formats kept
(DIB for the small sizes, PNG for 256) -- no resampling anywhere.
Contrast on the icon background improves from 4.72:1 to 5.38:1.

Author: sbryngelson