fix: Publish stage skipped due to broken stageDependencies output variable in 1ES template

[Saadnajmi]

Follow-up to #4093

PR #4093 fixed the not(${{ parameters.skipNpmPublish }}) compile-time/runtime boolean mismatch, but the Publish stage is still being skipped.

Root Cause

The remaining issue is the stageDependencies output variable reference:

eq(stageDependencies.Build.BuildAndPack.outputs['check.hasTarballs'], 'true')

Under 1ES Pipeline Templates, templateContext.outputs restructures the job internally. This breaks the stageDependencies reference path — the output variable resolves to empty, so eq('', 'true') → false, and the stage is always skipped.

Fix

1. Remove the cross-stage output variable dependency from the stage condition. The simplified condition is now:

   condition: and(succeeded(), eq(variables['Build.SourceBranch'], 'refs/heads/main'), ne('${{ parameters.skipNpmPublish }}', 'true'))

2. Move the tarball check into the Publish job — after downloading the artifact, verify tarballs exist and fail early with a clear error if they don't:

   - script: |
       echo "Downloaded tarballs:"
       ls -la $(System.DefaultWorkingDirectory)/_packed/
       if ! ls $(System.DefaultWorkingDirectory)/_packed/*.tgz > /dev/null 2>&1; then
         echo "##vso[task.logissue type=error]No tarballs found in _packed/"
         exit 1
       fi
     displayName: 'Verify downloaded tarballs'

This is more robust than relying on cross-stage output variables through the 1ES template layer.