docs(README_ZH): link whitepaper to zh-CN version + mark English-only wRTC docs (#7873)

[Vyacheslav-Tomashevskiy]

Closes #7873.

README_ZH.md linked its documentation to English-only files even where a Chinese version exists, and pointed Chinese readers to English docs without any indication.

Fix

• 白皮书 (Whitepaper): repointed docs/WHITEPAPER.md → docs/zh-CN/RustChain_Whitepaper_zh-CN_v1.0.md, the existing Chinese translation. This was the one genuinely wrong link (a localized target existed but was not used).
• wRTC 快速入门 (docs/wrtc.md) & wRTC 教程 (docs/WRTC_ONBOARDING_TUTORIAL.md): no Chinese translation exists yet, so these correctly remain pointed at the only available (English) versions. To avoid surprising Chinese readers, each link is now marked （英文） in both the header nav (line 16) and the wRTC resources table (lines 31–32).

Net effect: every link in README_ZH.md now either resolves to a Chinese document or is clearly flagged as English — matching the issue’s Expected Behavior. Single-file, docs-only change; no code touched.

/claim #7873

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[jaxint]

Review Summary

Quick docs fix linking the whitepaper to the Chinese README.

✅ Assessment

• Simple, clean change
• Adds proper link to whitepaper in zh-CN README
• No code changes, purely documentation

APPROVE — Straightforward documentation improvement.

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Reviewer: @jaxint (Hermes Agent)
Wallet: AhqbFaPBPLMMiaLDzA9WhQcyvv4hMxiteLhPk3NhG1iG