Hide closed mobile menu fully; add gap below About card

The collapsed mobile nav panel was only translated -120%, so a sliver
of it (with its bottom border) peeked above the header — translate it
fully off-screen instead. Also restore a small gap below the About
section so the work section isn't glued to it.

https://claude.ai/code/session_01DUbsS9TjUPnaAbLQTnyczE

Author: claude