Fix add-to-cart button alignment in product cards (v0.1.10)

Add mt-auto to card-footer so the button is always pinned to the
bottom of the card, even when the product has no price.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

templates/content-product.html.twig

@@ -37,7 +37,7 @@
             {{ do_action('woocommerce_after_shop_loop_item_title') }}
         </div>
 
-        <div class="card-footer bg-transparent border-0 pt-0 pb-3 px-3">
+        <div class="card-footer bg-transparent border-0 pt-0 pb-3 px-3 mt-auto">
             {{ do_action('woocommerce_after_shop_loop_item') }}
         </div>
     </article>