Generates a Google Shopping RSS 2.0 feed from your OpenCart 4 catalogue using Google's g: namespace: g:id, g:title, g:description, g:link, g:image_link, g:additional_image_link, g:price, g:sale_price, g:availability, g:condition, g:brand, g:gtin, g:mpn, g:product_type and g:identifier_exists. Identifiers are read from OpenCart 4.1's product_code table and from the legacy product columns, whichever is present, so SKU/EAN/UPC/JAN/ISBN/MPN survive both fresh installs and stores upgraded from 4.0. Specials come from product_discount rows, prices are converted into the feed currency and can include tax, and products are read from the database in batches of 250 so large catalogues do not exhaust memory. The feed route is guarded by a token and returns 404 without it.