Agent Skills: sfnext-custom-apis

End-to-end workflow for consuming custom SCAPI endpoints from a Storefront Next project — adding them as typed clients via `b2c sfnext scapi add custom`, discovering their schema, and calling them from loaders/actions/useScapiFetcher. Use this skill whenever the user wants to call a custom API from their Storefront Next app, gets a 404 or 401 when calling a custom endpoint from their sfnext loader, needs to add a custom API as a typed client in their storefront, asks about the full workflow from custom API cartridge to sfnext consumption, or says 'custom API in storefront next'. Also use when they ask how createApiClients exposes custom API methods or how to use useScapiFetcher with a custom endpoint. NOT for writing the custom API cartridge files (schema.yaml/script.js) from scratch — see b2c:b2c-custom-api-development. NOT for just checking registration status — see b2c-cli:b2c-scapi-custom.