Repository maintenance: fix cross-link 404s, add LICENSE, CI checks, and contribution governance

[anneheartrecord]

Housekeeping pass on the repo, plus two real defects found along the way.

Defects fixed

Every chapter cross-link 404'd on GitHub. All 56 of them were written as docs/<file>.md from inside docs/. With docsify's relativePath disabled those resolved from the site root, so the published site worked — but GitHub's file view resolved them to docs/docs/<file>.md. That is what anyone browsing the repo or working from a fork actually hits. Fixed by enabling relativePath and rewriting the links to same-directory relative form, correct in both contexts.

One link was dead everywhere. 12-Agent-Security-Design.md pointed at 13-啃完51万行源码的发现与Claude的封号机制.md, a filename that stopped existing when chapter 13 was renamed.

English chapter 01 was a third of the Chinese one — 5.2 KB against 15 KB — missing the source-leak background, what Claude Code is, how it differs from an agent framework, the six-step request journey, the industry comparison table, and the key-numbers table. Chapter 01 is where every English reader starts. Translated from the existing Chinese analysis: no new claims, same numbers, plus the four illustrations the Chinese side already had.

Added

• LICENSE — MIT, which both READMEs have declared since the first release without the file ever being committed, so GitHub showed the repo as unlicensed. Includes a scope note: no Claude Code source is redistributed here, and quoted excerpts remain their owners'.
• scripts/check_links.py — validates every local Markdown and image link and enforces the per-context link convention, so the cross-link bug cannot come back silently. Verified in both directions: passes clean on 188 links, and catches an injected broken link and an injected convention violation.
• scripts/check_bilingual.py — pairs chapters by number, flags any that exist in one language only or whose two sides have drifted apart in size. This is what surfaced the chapter 01 gap.
• GitHub Actions running both checks on push, on PRs, and weekly.
• CONTRIBUTING.md / CONTRIBUTING_EN.md — states that factual corrections are wanted over new content, and sets an evidence bar: source path plus symbol, reproducible steps, or official documentation.
• CODE_OF_CONDUCT.md — Contributor Covenant 2.1.
• Issue templates for chapter corrections, version drift, and new chapter proposals; drift reports carry the upstream version observed. Plus a PR template.
• Version coverage tables in both READMEs, recording which source snapshot the analysis was verified against instead of leaving readers to guess.
• CHANGELOG.md.

Also

• .idea/ dropped from version control.
• The two READMEs were out of sync; the Chinese side was missing the git-history paragraph and the reproduction steps the English side had.

Verification

$ python3 scripts/check_links.py
✓ 188 local links across 32 files, all resolve

$ python3 scripts/check_bilingual.py
✓ 13 chapters, both languages present and comparable

No chapter conclusions were changed. Re-verifying chapter content against current upstream is tracked separately.