docs: bilingual README (en + zh-CN)

[Pigbibi]

Summary

Documentation-only change. Aligns README.md and README.zh-CN.md with the organization documentation style guide.

Why

The READMEs used a repository-local layout and wording that did not follow the org style guide, and the English and Simplified Chinese files did not mirror each other section for section.

Changes

• Rewrote both READMEs to the required section skeleton (Status, What this is, What this is not, Quick start, Configuration, Repository layout, Contributing, Security, License).
• Added the standard language switcher line at the top of each file.
• Added a configuration table listing the supported proxy environment variables with required and default columns.
• Removed internal role, boundary, and lifecycle-policy notes and stale doc links.
• Confirmed the two files have the same sections in the same order with the same commands and facts.

Testing

• Ran the style guide section 13 grep list against both files; no matches for home paths, bucket URIs, personal subdomains, 40-character hex strings, status tables, dated audit titles, or process narration.
• Verified no personal accounts, emails, private hosts, or secret names appear in either file.
• Verified every relative link resolves to an existing file.

Risk and rollback

Docs only, no runtime or code impact. Revert by restoring the previous README revisions.

Breaking changes

none