docs: add a language switcher to both READMEs

[jingjingzhang1]

What

Adds a pair of shields.io badge buttons near the top of both READMEs so
readers can switch between the English and Simplified Chinese versions.

Why

README.zh-CN.md already linked back to the English README, but
README.md had no link to the translation at all — the Chinese README was
effectively unreachable from the repository landing page, which is where
most readers arrive.

Details

• The badge for the page you are currently on is teal (0F766E, matching
  the existing Documentation badge) and carries the translate glyph; it is
  intentionally not a link.
• The other language is a grey (555555) clickable badge.
• Placement is identical in both files: directly below the section-nav
  line, matching where the Chinese README already had its text switcher.
• Docs-only change; no code or tests touched.

Summary by CodeRabbit

• Documentation
  • Added a language switcher to the English README header, with an active English badge and a link to the Simplified Chinese translation.
  • Updated the Simplified Chinese README header to use badge-style language links, including a link back to the English README.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Team

Run ID: 12ff832b-4e24-4dd9-ac3d-7864d2cefb8f

📥 Commits

Reviewing files that changed from the base of the PR and between f346509 and 7628577.

📒 Files selected for processing (2)

• README.md
• README.zh-CN.md

Included review availability: Your plan provides up to 2 included reviews per hour; 1 remains after this review.

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📝 Walkthrough

Walkthrough

The README files now provide badge-style language navigation between English and Simplified Chinese.

Changes

README language switcher

Layer / File(s)	Summary
Update language switcher badges README.md, README.zh-CN.md	The English README adds an active English badge and a link to the Simplified Chinese README. The Simplified Chinese README uses badge images for both languages and links English to README.md.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to 76285

The README language badges provide consistent navigation between English and Simplified Chinese without affecting runtime behavior or deployment.

Suggested reviewers: claude

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main documentation change: adding a language switcher to both README files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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