site: packs.html uses index.html as exact template

User reported the /packs page had different width, logo style, and
nav shape. Rewrote to verbatim copy index.html's masthead + .shell
(1480px) + wordmark + .nav + .foot. Hero / packs grid / how section
keep packs-specific content with the home-page rhythm.

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

Author: Tomas Pflanzer