Fix validateBuild failing due to npm output capture

Ensure Invoke-Npm streams output to host and returns only exit code.

Co-authored-by: Cursor <cursoragent@cursor.com>

infra/scripts/deploy-dev-to-prod.ps1

@@ -55,7 +55,10 @@ function Invoke-Npm {
         $args += '--'
         $args += $ExtraArgs
     }
-    & npm @args
+    # Prevent npm stdout/stderr from becoming pipeline output for the caller.
+    # Without this, callers that assign the function result to a variable can
+    # accidentally capture npm's printed output instead of only exit code.
+    & npm @args 2>&1 | Out-Host
     return $LASTEXITCODE
 }