[codex] Add open-source README overview

[Pigbibi]

Summary

• Add a bilingual investment-risk notice near the top of the README.
• Add an open-source oriented overview explaining what the repository does, current status, quick start, safe deploy/operation path, and evidence/performance boundary.
• Keep the existing detailed runbooks and historical notes below the new entry section.

Validation

• README coverage script checked Chinese and English risk notices plus overview, quick start, deploy/operate, and evidence sections.
• git diff --check

Notes

This PR is documentation-only and does not change runtime behavior, workflows, credentials, or strategy defaults.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Fix the quick-start extra before publishing it

In a fresh checkout this command does not install pytest, because pyproject.toml defines no test extra (pytest only appears in requirements.txt). Pip will install the package without those test dependencies, so the next documented step, python -m pytest -q, can fail for users following the README exactly unless pytest already happens to be installed.

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