Fix shop/related/wishlist grids not equalizing card heights

ProductCard already has a h-full + flex-1 spacer specifically to keep
every card in a row the same height regardless of content (title wrap,
subline wrap, low-stock line) — but all three grids using it set
items-start on the grid container, which overrides the default stretch
and silently defeats that. A product whose subline wraps to 2 lines made
its card taller than its row siblings instead of them matching. Dropping
items-start (default items-stretch) fixes all three call sites.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J1Hu5bZ1kZUgKhab6yNwCt

app/konto/merkliste/components/MerklisteGrid.tsx

@@ -39,7 +39,9 @@ export function MerklisteGrid({
   }
 
   return (
-    <RevealGroup className="grid items-start grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 gap-6 w-full">
+    // No items-start — see ProductGrid.tsx's own comment on why that
+    // silently defeats ProductCard's h-full equal-height design.
+    <RevealGroup className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 gap-6 w-full">
       {visibleEntries.map(({ item, product }) => (
         <RevealItem key={`${product.id}-${item.variant}`}>
           <ProductCard