fix(site): restore missing dprod.jpg in /spec/main/ archive

The frozen OMG 1.0 archive references ./assets/dprod.jpg in its
index.html but the file wasn't included when the archive was
copied in, so the logo rendered as a broken image at /dprod/spec/main/.
Add the same logo file used by the live spec.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jgeluk