Expose Shopify handle.js data as a Preact hook: `useShopifyProduct(handle: string)`

[timowestnosto]

Description:
Create a new Preact hook, useShopifyProduct(handle: string), that fetches and exposes product data from Shopify’s handle.js endpoint. This will allow components to easily retrieve and use Shopify product data by handle within the Preact application.

Acceptance Criteria:

• Implement a hook useShopifyProduct(handle: string) in src/hooks/useShopifyProduct.ts.
• The hook should fetch product data from /products/${handle}.js.
• The hook should return loading, error, and product data states.
• The hook should cache results per handle to avoid unnecessary network requests.
• Add unit tests for the hook to cover loading, error, and success states.
• Update documentation to describe usage of the new hook.

References:

• Shopify product handle.js endpoint documentation
• Example usage:

  const { product, loading, error } = useShopifyProduct("my-product-handle")