ci(windows): persist validated ISO to stable runner path

RUNNER_TEMP is ephemeral; copy the validated build output to C:\silvermetal\out\
so it can be retrieved out of band (e.g. for VM boot-testing).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/build-iso-windows.yaml

@@ -102,6 +102,15 @@ jobs:
         run: |
           .\windows\tests\Assert-IsoStructure.ps1 -IsoPath "$env:RUNNER_TEMP\out\SilverMetal-Enhanced-Windows.iso"
 
+      - name: Persist build output to stable path
+        shell: pwsh
+        run: |
+          # RUNNER_TEMP is per-job/ephemeral. Keep the latest validated build at a
+          # stable path so it can be retrieved (e.g. for VM boot-testing) out of band.
+          New-Item -ItemType Directory -Force 'C:\silvermetal\out' | Out-Null
+          Copy-Item "$env:RUNNER_TEMP\out\*" 'C:\silvermetal\out\' -Force
+          Get-ChildItem 'C:\silvermetal\out' | ForEach-Object { Write-Host $_.Name }
+
       - name: Upload SBOM + SHA (always)
         uses: actions/upload-artifact@v3
         with: