Fix release workflow tag-version check by exporting TAG_VERSION

[Copilot]

The release workflow failed on tag pushes because TAG_VERSION was set in shell scope only, while the inline Python check reads from os.environ. This change makes the variable available to Python and adds a workflow test assertion to prevent regressions.

Changes proposed in this pull request:

• Workflow fix
  • Export TAG_VERSION before invoking the inline Python version/tag consistency check in .github/workflows/release.yml.
  • Example:

    export TAG_VERSION="${GITHUB_REF_NAME#v}"
    python - <<'PY'
    import os
    expected = os.environ["TAG_VERSION"]
    PY

• Regression coverage
  • Update tests/test_release_workflow.py to assert the workflow includes export TAG_VERSION="${GITHUB_REF_NAME#v}".

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