Previously combined as a single "556-223" caliber. Now tracked separately
with dedicated scraper URLs per retailer. Also fixes broken URLs for
Lucky Gunner, True Shot Ammo, and Palmetto State Armory.
Add True Shot Ammo (Shopify JSON), Palmetto State Armory (Magento HTML),
Bulk Ammo (Magento HTML), and Natchez Shooters Supply (GraphQL API).
Extends scraper infrastructure with HttpClient.post_json/3 and an
optional fetch/2 callback on the Scraper behaviour for scrapers that
need custom HTTP flows (e.g. GraphQL POST requests).
