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]

Install test extras before running pytest

In the documented “fresh clone” path, python -m pip install -e . only installs runtime dependencies, while this repo declares pytest under the test optional extra in pyproject.toml. On a clean environment without pytest already installed, the very next command fails before any tests run. Please keep the previous python -m pip install -e '.[test]' guidance, and mirror the same fix in README.zh-CN.md.

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