VCST-5777-vcst-qa-deployment

[vc-ci]

ci: Automated update vc-frontend from PR 2451 VirtoCommerce/vc-frontend#2451

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Note

Low Risk
Single configuration URL swap for a prerelease theme package; no application logic changes.

Overview
Updates the B2B Vue theme artifact used for VCST QA deployment by changing the URL in theme/artifact.json from the vc-theme-b2b-vue build tied to frontend PR 2449 to the build from PR 2451 (2.56.0-pr-2451-8ba8-8ba8bd04).

This is an automated bump so the deploy-theme workflow (which reads ARTIFACT_URL from that file) pulls the theme package produced by vc-frontend#2451.

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