feat(i18n): add Korean (ko) localization across docs and web app

[meohyun2]

Summary

Adds a full Korean translation layer across every i18n-enabled surface of the project.

• Root README → new README-ko.md; existing README.md / README-zh.md / README-ja.md get [한국어](./README-ko.md) added to their cross-language headers.
• Session docs → new docs/ko/ with full Korean translations of all 12 session docs (s01-s12). Replaces the previously empty docs/kr/ directory; ko matches ISO 639-1 and the existing en / zh / ja naming convention.
• Web i18n → new web/src/i18n/messages/ko.json mirroring the en.json key tree.
• Locale wiring — "ko" registered in:
  • web/src/lib/i18n.tsx, web/src/lib/i18n-server.ts
  • web/src/app/[locale]/layout.tsx (locales, metaMessages)
  • web/src/components/layout/header.tsx (new 한국어 button)
  • web/src/types/agent-data.ts (DocContent.locale union)
  • web/scripts/extract-content.ts (localeDirs, detectLocale return type)
• Generated data — web/src/data/generated/{docs,versions}.json regenerated to include the 12 Korean docs, so the Next.js static export emits /ko/, /ko/timeline/, /ko/compare/, /ko/layers/, and /ko/s01..s12 (plus the /diff sub-routes).

Translation conventions

• Tone: professional 존댓말 (formal-polite) — matches the style of Korean tech books / engineering blogs.
• Widely-known technical terms are kept in English when the Korean dev community uses them in English, wrapped in natural Korean grammar:
  agent, harness, loop, tool, subagent, skill, context, compact, task, worktree, mailbox, FSM, JSONL, Bash, RLHF, GOFAI, …
• First-mention glosses added in parentheses for terms a Korean reader may find unfamiliar — e.g.:
  • harness (하네스 — 모델을 감싸 실제 환경에서 동작하게 해주는 코드 레이어)
  • Agency (행위자성 — 인지·추론·행동의 능력)
  • FSM (Finite State Machine, 유한 상태 기계)
  • worktree (워크트리 — git worktree, 같은 저장소를 여러 디렉터리에 동시에 체크아웃하는 기능)
• Code blocks, ASCII diagrams, file paths, function/variable names, URLs, and proper nouns are preserved verbatim.
• Doc line counts match the English originals exactly (s01: 116, s02: 99, s03: 96, s04: 94, s05: 108, s06: 124, s07: 131, s08: 107, s09: 125, s10: 106, s11: 142, s12: 121) to keep the mental-model section structure aligned.

Verification (already run locally)

• cd web && npm run extract → Found 48 doc files across 4 locales, 48 docs
• cd web && npx tsc --noEmit → 0 errors
• cd web && npm run build → succeeds, emits /ko/* and /ko/sXX/* static routes alongside the existing locales
• grep -c '"locale": "ko"' web/src/data/generated/docs.json → 12
• head -1 README-ko.md → [English](./README.md) | [中文](./README-zh.md) | [日本語](./README-ja.md) | [한국어](./README-ko.md)

Test plan

A full manual QA scenario lives at docs/ko/TEST_SCENARIOS.md. Highlights:

• docs/kr/ removed; docs/ko/ contains 12 session docs + TEST_SCENARIOS.md
• All 4 root READMEs carry the 4-language header row
• npm run extract && npx tsc --noEmit && npm run build clean in web/
• npm run dev → locale switcher shows EN | 中文 | 日本語 | 한국어 (desktop + mobile)
• /ko, /ko/timeline, /ko/compare, /ko/layers, /ko/s01../ko/s12 all render with Korean UI strings
• On /ko/sXX the Learn tab renders docs/ko/sXX-*.md content (Korean prose, English code preserved)
• Regression: /en, /zh, /ja still render correctly
• Dark mode toggle still works on /ko/*

Out of scope

• agents/sXX_*.py source files (English identifiers / comments preserved; not user-facing i18n).
• skills/*/SKILL.md (Anthropic Agent SDK style — no multi-language layer).
• Config files (.env, requirements.txt, package.json).

🤖 Generated with Claude Code

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