Agent Skills: sfnext-extensions

Build extensions for Storefront Next using target-config.json, target points, extension routes, and translation namespaces. Use when creating modular features, inserting components into UI targets, adding extension routes, adding a section to an existing page, or using SFDC_EXT_ integration markers. Covers the base-audit decision gate (deciding whether to extend at all vs token/variant override), extension structure, targetId configuration, and extension registration in src/extensions/config.json.