fix: correct English tutorial count from 34 to 40

[KieranGao]

Problem

The English homepage (en/index.md) and README (README_en.md) claim the project has "34 architecture-thinking chapters." The project actually has 40 tutorial chapters in Chinese (tutorial/01- through tutorial/40-); only 34 have been translated to English so far. The current wording may misleads English readers into thinking the entire curriculum is 34 chapters, rather than "40 total, 34 translated."

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英文首页（en/index.md）和 README（README_en.md）声称项目有"34 章架构思维教程"。实际上项目共有 40 章中文教程（tutorial/01- 到 tutorial/40-），其中只有 34 章已翻译为英文。当前的措辞可能会误导英文读者，让他们以为整个课程体系只有 34 章，而非"共 40 章，已翻译 34 章"。

Changes

en/index.md (2 fixes):

• Tagline: 34 architecture-thinking chapters → 40 architecture-thinking chapters (34 translated to English)

• Bilingual notice: All 34 tutorial chapters → 34 of 40 tutorial chapters, all 31 templates

README_en.md (1 fix):

• Line 195: all **34 tutorial chapters** → **34 of 40 tutorial chapters**

Verification

• All changes are text-only (no links, no structure, no code modified)
• No new files added, no files deleted
• pnpm docs:build dead-link check is not affected (no links changed)

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• 所有改动仅为文字修正（无链接、无结构、无代码变更）
• 未新增、未删除任何文件
• pnpm docs:build 死链检查不受影响（未改动任何链接）

[study8677]

Thank you for catching and fixing the tutorial-count mismatch! This PR has been merged. I made a small follow-up in 437ba1b to replace “Fully bilingual” with “English translation coverage,” keeping the wording consistent with 34 of 40 chapters being translated. Really appreciate the contribution!