Simplify NuGet publishing to nuget.org

[thebuilder]

Summary

• remove the int.nugettest.org publishing job, credentials, environment, and manual workflow input
• publish both GitHub prereleases and stable GitHub Releases to nuget.org through one trusted-publishing job
• require GitHub's release type to match the SemVer tag: prerelease releases need prerelease versions, and stable releases need stable versions
• simplify the maintainer release documentation around the single-gallery workflow

Why

The test-gallery path introduced a second policy and routing model without providing useful protection for the release process. A GitHub prerelease has already established TheBuilder.WebAnalytics prerelease publishing on nuget.org, so the workflow now treats that as intentional behavior and removes the integration-gallery complexity.

Impact

Publishing a GitHub prerelease such as v0.2.0-preview.1 publishes that prerelease package to nuget.org. Publishing a stable GitHub Release such as v0.2.0 publishes the stable package to nuget.org. There is no manual publish trigger or test-gallery configuration.

Verification

• parsed the workflow as valid YAML
• confirmed no int.nugettest.org, nuget-test, manual-dispatch, or test-publish references remain
• exercised prerelease/stable release flags against prerelease/stable SemVer values
• verified workflow and documentation diff checks