chore: suppress PyPI publishing via hatch-native config

[Copilot]

Summary

Adds the hatch-native [tool.hatch.publish.index] disable flag to complement the existing Private :: Do Not Upload classifier, providing an explicit, tool-level guard against accidental PyPI publishes.

Changes

• Added [tool.hatch.publish.index] with disable = true to pyproject.toml — prevents hatch publish from targeting the PyPI index at the tool level, independent of workflow-level checks

[tool.hatch.publish.index]
disable = true

Testing

• make test passes locally
• make fmt has been run
• New tests added (or explain why not needed) — config-only change, no logic to test

Checklist

• Commit messages follow the Conventional Commits format
• Documentation updated if behaviour changed
• make deptry passes (no unused or missing dependencies)

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[Copilot]

Pull request overview

Adds a Hatch configuration flag intended to explicitly disable publishing to the default index (PyPI), complementing the existing Private :: Do Not Upload classifier safeguard.

Changes:

• Add [tool.hatch.publish.index] configuration with disable = true in pyproject.toml to guard against hatch publish targeting PyPI.