ci(windows): wire SignPath test-signing for portable bundle

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).

.github/workflows/build_all.yml

@@ -13,6 +13,8 @@ on:
      - 'localization/**'
      - 'resources/**'
      - ".github/workflows/build_*.yml"
+     - 'signpath/**'
+     - 'scripts/*.ps1'
      - 'scripts/flatpak/**'
 
   pull_request:
@@ -26,9 +28,11 @@ on:
      - '**/CMakeLists.txt'
      - 'version.inc'
      - ".github/workflows/build_*.yml"
+     - 'signpath/**'
      - 'build_linux.sh'
      - 'build_release_vs2022.bat'
      - 'build_release_macos.sh'
+     - 'scripts/*.ps1'
      - 'scripts/flatpak/**'