perf(albums): bump infinite-scroll prefetch margin from 200px to 1500px (#247)

The IntersectionObserver sentinel triggered the next page only when it
came within 200px of the viewport — by the time the user had scrolled
that far, they were already at the very edge waiting for the request.

Bumping rootMargin to 1500px (~1.5 screens at typical heights) prefetches
ahead of the scroll instead of behind it, so the next batch of albums is
visibly already there when the user reaches them.

Co-authored-by: Psychotoxical <dev@psysonic.app>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/Albums.tsx

@@ -186,7 +186,9 @@ export default function Albums() {
   useEffect(() => {
     const observer = new IntersectionObserver(
       entries => { if (entries[0].isIntersecting) loadMore(); },
-      { rootMargin: '200px' }
+      // Prefetch ~1.5 screens ahead so the user never visibly waits at the
+      // bottom of the grid. 200px caught the user at the very edge.
+      { rootMargin: '1500px' }
     );
     if (observerTarget.current) observer.observe(observerTarget.current);
     return () => observer.disconnect();