Run WACK in Microsoft Store CI

[StephanOrgiazzi]

Summary

• run the official Windows App Certification Kit (appcert.exe) against the generated Store MSIX
• fail Store CI if WACK reports a failing test or non-PASS overall result
• keep the generated WACK XML report as a GitHub Actions artifact even when certification fails

This gives every Store package a local certification pass before it is uploaded to Partner Center.