Fetches all products and variants from Shopify API, creates local
Products, Packings and ProductSizes with shopify_variant_id, and
fills ProductInventory rows to match Shopify's inventory_quantity.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Log clear hint for 403 (IP whitelist), 401, 429, 5xx.
Commands exit with failure and print error when API returns no data.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>