feat(vs-extension): API Browser shopper-schema → sfnext scapi add

[clavery]

Summary

• Right-click a Shopper schema in the API Browser to run pnpm sfnext scapi add <apiFamily> <apiName> <apiVersion> in an integrated terminal.
• Menu entry is gated on Storefront Next workspace detection via @salesforce/b2c-tooling-sdk/discovery (detectWorkspaceType) — only appears when b2c-dx.isStorefrontNext context is true.
• Tree items now expose apiSchema-shopper / apiSchema-admin context values; classification uses an isShopperSchema() helper that checks both apiFamily and apiName for shopper* (case-insensitive) so APIs that come back as apiName=\"shopper-products\" are classified correctly.
• Detection result, schema family distribution, sample entries, and command invocation are all logged to the B2C DX output channel for diagnosis.

Notes

• Upcoming `b2c-cli` plugin work (feat: add b2c sfnext JIT plugin for Storefront Next integration #455) will replace `pnpm sfnext` with a first-class `b2c` subcommand — no extension change needed once the plugin ships, since the integrated terminal command can be updated in-place.
• No new SDK surface — uses the existing `detectWorkspaceType` already consumed by the MCP server.