Add SignPath artifact configuration (windows-portable-v1) signing only the
first-party binaries orca-slicer.exe and OrcaSlicer.dll, plus verification
and inventory scripts. The Windows build job uploads the unsigned portable
bundle, submits it to SignPath (test-signing), verifies the returned
signatures, and rebuilds the installer/zip from the signed binaries.
project-slug matches the SignPath project (OrcaSlicer).
