Optimize public repository layout

[Chihvane]

Summary / 摘要

• Optimized the public repository layout around reader trust and discoverability: root licenses, citation metadata, public docs, social preview asset, and README first-screen navigation.
• Removed public Markdown links into .internal/ and updated readiness checks to enforce that boundary.
• Updated Chapter 1 public version maps so platform-package notes no longer link into internal authoring paths.
• Deliberately did not start the Chapter 2 English translation project.

Language Surface / 语言表面

• English
• 简体中文
• Both / 两者
• Not language-specific / 非语言相关

Public Surface Changed / 变更的公开表面

• README / repository map
• GitHub Pages
• GitHub Wiki source
• Chapter package
• Citation evidence
• Publishing package
• Whitepaper / glossary
• Repository configuration

Checks / 检查

• make -f .internal/engineering/Makefile check
• Canonical PDF remains authoritative for Chapter 1 changes
• No private implementation details or sensitive operational traces added
• Citation evidence updated if cited claims changed
• Bilingual links still point to the matching language edition

Verification Details

• Ran readiness on a clean detached worktree at commit 44bdca8: passed.
• Ran public Markdown/HTML internal-link scan: no links into .internal/ remain outside .internal/.
• Confirmed chapter2/final-draft-v7.3/en/ was not created.
• Confirmed assets/social-preview/og.png is 1280 x 640.
• Applied repo description and topics via gh repo edit.

TODO(owner)

• Upload assets/social-preview/og.png in GitHub repository Settings -> Social preview.
• Decide whether Chapter 2 v7.3 should get a canonical PDF in a separate pass.
• Decide when to open the Chapter 2 English translation/proofreading workflow; this PR intentionally does not include it.
• Create tagged GitHub Releases for chapter artifacts after release asset policy is finalized.