feat(checkout): CHECKOUT-10368 Migrate company address search to customer.activeCompany

[bc-peng]

Jira: CHECKOUT-10368

What/Why?

Storefront GraphQL is removing the root-level company query field and standardizing on customer.activeCompany as the single entry point for B2B company data.

This PR migrates the SearchCompanyAddresses query to the new shape.

Rollout/Rollback

Rolls out with the next SDK release; no feature flag — customer.activeCompany.addresses is already live in production SFGQL and resolves identically to the root company field (same underlying data and auth gate). Must be live in production before the storefront team removes the root company field (B2B-5578) — sign-off happens on that ticket after verification.

Rollback: revert this PR and release; the root company field still exists until B2B-5578 proceeds.

Testing

Manually tested the changes alongside the checkout-js changes.

🤖 Generated with Claude Code

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Note

Medium Risk
Breaking SDK contract for B2B address search consumers (company → customer.activeCompany); timing must stay ahead of SFGQL removing the root company field.

Overview
Prepares the checkout SDK for removal of the root storefront GraphQL company field by routing B2B company address search through customer.activeCompany instead.

The SearchCompanyAddresses operation now queries customer { activeCompany { addresses(...) } }, and derived types (CompanyAddressSearchResult, CompanyCompany) plus CheckoutService.searchCompanyAddresses docs/tests expect customer / customer?.activeCompany rather than company. This is a breaking response shape for callers that read result.company.

packages/core/schema/storefront.graphql is updated in the same change (including the new ActiveCompany type on Customer and many other SFGQL additions); codegen for the search query picks up the new path from that schema.

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