docs: split bilingual open-source readmes

[Pigbibi]

Summary

• replace the mixed-language README with an English-only open-source entry point
• add a separate Chinese README.zh-CN.md with the same project overview structure
• include explicit risk notices, quick start, deployment guidance, and evidence boundaries

Validation

• verified README.md contains no Chinese characters
• verified README.zh-CN.md exists and contains the Chinese risk notice
• verified only README.md and README.zh-CN.md changed

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Include pytest in the fresh-clone quick start

In a clean environment, following this quick start installs only requirements.txt, but that file does not include pytest, so the next command fails with No module named pytest. I checked the CI install step, which adds pytest separately from requirements.txt, so the README should either install the test runner explicitly or point users at the same setup used by CI; the Chinese README mirrors the same broken sequence.

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