Hide the synthetic Default Title option on single-SKU products

Shopify gives every single-variant product one option named Title with the
lone value Default Title. It isn't a real choice, so filter it out of the
product detail options, the cart line summaries, and the payload the store
assistant sees. Variant matching still reads the raw selectedOptions, so
single-SKU products keep resolving their variant.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EuRVxuyMUTzWKXW8P5Tn8A

components/shopify/product-detail/product-detail-info.tsx

@@ -5,6 +5,7 @@ import { RiSubtractLine, RiAddLine } from '@remixicon/react';
 import ShopPayButton from '@/components/shopify/shop-pay-button';
 import type { ProductOption, ProductOptionValue } from '@/hooks/use-shopify-products';
 import { isSwatchOptionName, swatchColorForName } from '@/config/swatches';
+import { isDefaultTitleOption } from '@/services/shopify/catalog';
 
 interface ProductPrice {
   amount: string;
@@ -103,9 +104,10 @@ const ProductDetailInfo: React.FC<ProductDetailInfoProps> = ({
     isSwatchOptionName(option.name);
 
   // Some products return Size before Color; show the swatches first either way.
-  const orderedOptions = [...(product.options ?? [])].sort(
-    (a, b) => Number(isSwatchOption(b)) - Number(isSwatchOption(a))
-  );
+  // Single-SKU products expose a synthetic `Title: Default Title` option — drop it.
+  const orderedOptions = [...(product.options ?? [])]
+    .filter((option) => !isDefaultTitleOption(option))
+    .sort((a, b) => Number(isSwatchOption(b)) - Number(isSwatchOption(a)));
 
   // `optionValues` carries the swatch data; fall back to plain `values`.
   const optionValuesFor = (option: ProductOption): ProductOptionValue[] =>