ci: fail loud on velopack errors, guard release assets

scripts/release/package-velopack.ps1

@@ -66,6 +66,7 @@ $publishArgs = @(
 Write-Host "dotnet publish..." -ForegroundColor Cyan
 if (-not $WhatIf) {
     & dotnet $publishArgs
+    if ($LASTEXITCODE -ne 0) { throw "dotnet publish failed ($LASTEXITCODE)" }
 } else {
     Write-Host "[WhatIf] dotnet $publishArgs"
 }
@@ -85,6 +86,7 @@ $vpkArgs = @(
 Write-Host "vpk pack..." -ForegroundColor Cyan
 if (-not $WhatIf) {
     & dotnet tool run vpk $vpkArgs
+    if ($LASTEXITCODE -ne 0) { throw "vpk pack failed ($LASTEXITCODE)" }
 } else {
     Write-Host "[WhatIf] dotnet tool run vpk $vpkArgs"
 }