When the nav is hidden (auto-hidden after scrolling past 50px), a
fixed-position hover sensor at the top of the viewport catches mouseenter
and slides the nav back in. Moving the mouse away from the nav slides it
back out.
Gated by `@media (hover: hover)` via JS matchMedia so touch devices are
unaffected — the existing single-tap toggle stays the only way to show
the nav there.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
yiekheng
f3d71a5423