Replace scroll-direction nav reappear with a one-shot scroll-down hide
plus tap-on-image toggle. Distinguish tap from scroll on touch via
touchstart/touchmove tracking so swipes don't re-show the nav.
Discourage casual image saving with contextmenu prevent, draggable=false,
select-none, and -webkit-touch-callout:none. Add 10.8.0.2 to
allowedDevOrigins for VPN dev access.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
