fix(media): lightbox pages via native scroll-snap so swipe direction matches the gallery

The sliding-track lightbox translated a prev/current/next pane set by
hand and got swipe direction wrong on touch. Replace it with the same
mechanism the inline gallery uses: a native horizontal scroll-snap
pager with one full-screen pane per image. The browser handles touch
direction, momentum and snapping, so swiping in the lightbox feels
identical to the feed carousel by construction. Mouse drag-to-swipe
reuses the gallery's pointer rules; offscreen panes preload their
images; navigation clamps at the ends (matching the gallery) instead
of wrapping, and the chevrons hide at the edges accordingly.

Author: dmnyc

package.json

@@ -1,7 +1,7 @@
 {
   "name": "zap.cooking",
   "license": "MIT",
-  "version": "4.2.491",
+  "version": "4.2.492",
   "private": true,
   "scripts": {
     "dev": "vite dev",