fix(gallery): sync thumbnail strip to the active image (DECO-5280)

When the main image advances (arrow/swipe/keyboard), scroll the active dot
into view so the thumbnail strip keeps the current thumb visible — matters for
the PDP gallery with many images.

- Slider observer: dot?.scrollIntoView({ block: "nearest", inline: "nearest" }).
  `nearest` is a no-op for small dot rows (Carousel/Logos) and never scrolls the
  page; only scrollable strips (gallery thumbnails) move.

The issue's other two parts already work: variant→image switch (variant nav
reloads page.product → filterImagesForVariant) and zoom-modal prev/next arrows.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JonasJesus42

src/components/ui/Slider.tsx

@@ -123,6 +123,11 @@ function useSlider(
           if (entry.isIntersecting) {
             dot?.setAttribute("disabled", "");
             dot?.setAttribute("aria-current", "true");
+            // Keep the active dot in view — matters for scrollable thumbnail
+            // strips (e.g. the PDP gallery with many images). `nearest` only
+            // scrolls when needed, so it's a no-op for the small dot rows of
+            // the Carousel/Logos sliders and never scrolls the page.
+            dot?.scrollIntoView({ block: "nearest", inline: "nearest" });
           } else {
             dot?.removeAttribute("disabled");
             dot?.removeAttribute("aria-current");