itdove/devaiflow#367: Add TestPyPI workflow for safe release testing

[itdove]

This PR does not need a corresponding Jira item.
Related GitHub Issue: #367

Description

This PR adds a TestPyPI workflow for safe release testing before publishing to production PyPI. The new GitHub Actions workflow allows maintainers to test the full release process (build, publish, install) in a sandboxed environment, reducing the risk of publishing broken releases.

Changes include:

• New .github/workflows/publish-test.yml workflow that builds and publishes to TestPyPI on manual trigger
• Updated RELEASING.md with TestPyPI testing procedures
• Enhanced docs/developer/publishing-to-pypi.md with TestPyPI workflow instructions
• Updated AGENTS.md with release testing guidance

The workflow is manually triggered via GitHub Actions UI and provides a safe way to validate the entire release pipeline before pushing to production PyPI.

Assisted-by: Claude

Testing

Steps to test

1. Pull down the PR
2. Navigate to the repository's Actions tab on GitHub
3. Select the "Publish to TestPyPI" workflow
4. Click "Run workflow" and trigger it manually on the current branch
5. Verify the workflow completes successfully and publishes to TestPyPI
6. Check the TestPyPI package page at https://test.pypi.org/project/devaiflow/ to confirm the package was published
7. (Optional) Test installation from TestPyPI: pip install --index-url https://test.pypi.org/simple/ devaiflow
8. Review the updated documentation in RELEASING.md and docs/developer/publishing-to-pypi.md for accuracy

Scenarios tested

• Workflow file syntax validation
• Documentation accuracy and completeness
• Manual workflow trigger functionality (via GitHub Actions UI)

Deployment considerations

• This code change is ready for deployment on its own
• This code change requires the following considerations before being deployed:

Note: This workflow requires TEST_PYPI_API_TOKEN to be configured as a repository secret in GitHub Actions for the workflow to successfully publish to TestPyPI.