VCST-5647,VCST-5590,VCST-5592,VCST-5588,VCST-5587-vcst-qa-deployment

[vc-ci]

ci: Automated update vc-frontend from PR 2437 VirtoCommerce/vc-frontend#2437

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Note

Low Risk
Single configuration URL change for QA theme packaging; no application or security logic is modified.

Overview
Updates theme/artifact.json so deploy workflows pull a prerelease storefront theme package instead of the 2.55.0 GitHub release.

The artifact URL changes from vc-theme-b2b-vue-2.55.0 on GitHub releases to vc-theme-b2b-vue-2.56.0-pr-2437-315c-315cd30c on Azure blob storage, aligning this branch with vc-frontend PR 2437 for VCST QA theme deployment (deploy-theme.yml reads this file for ARTIFACT_URL).

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