shop: revert product card tone back to cream

The brand-green media wash was only meant for the homepage's
3-product teaser, not the full shop catalogue. Reverts ShopPage's
ProductCard tone from `brand` → `cream` so shop cards keep the
cream image area / paper body that the rest of the catalogue uses.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/ShopPage.vue

@@ -241,7 +241,7 @@ onBeforeUnmount(() => {
             :image="product.image"
             :image-alt="product.title"
             :href="product.href"
-            tone="brand"
+            tone="cream"
             :in-stock="product.inStock"
             :cta-variant="i % 2 === 1 ? 'accent' : 'primary'"
             @add="onAdd(product)"