docs(l10n): add ko-kr, ja-jp, zh-cn, es-es, pt-br translations of the full course - #121

Summary

Adds full localization of the course documentation into 5 languages under localization/<locale>/, mirroring the original directory structure. Each translated chapter, README, and appendix is a standalone document; images continue to point at the originals in the repo-root images/ folder. A new 🌐 Use Your Preferred Language section and matching TOC entry land in the root README.md so readers can switch languages from the landing page.

Locales

• ko-kr — 한국어
• ja-jp — 日本語
• zh-cn — 中文（简体）
• es-es — Español
• pt-br — Português (Brasil)

Each locale ships 13 documents (root README + chapters 00–07 + appendices), for 65 translated files in total.

What's localized

• Root README (course intro, prerequisites, family overview, course structure, quick reference, language switcher)
• Chapters 00-quick-start through 07-putting-it-together
• appendices/README.md, appendices/additional-context.md, appendices/ci-cd-integration.md

What's intentionally NOT localized

• Top-level project files: AGENTS.md, CODE_OF_CONDUCT.md, CONTRIBUTING.md, GLOSSARY.md, SECURITY.md, SUPPORT.md
• samples/** (code samples and supporting files)
• .github/** (templates, workflows)

Quality work performed

After the initial machine-assisted translation pass, the following corrections were applied across every locale to ensure rendered output is faithful and links resolve:

1. Image paths — chapter-local images now resolve correctly via ../../../<chapter>/images/..., repo-root shared images via ../../../images/... from chapters and ../../images/... from each locale's root README.
2. Repo-root references — links to GLOSSARY.md, LICENSE, etc. updated to ../../../GLOSSARY.md style from chapter files.
3. Markdown emphasis + link order — **[text](url)** rewritten to [**text**](url) so GitHub renders the bold inside the link (≈115 fixes).
4. Internal anchor localization — every [text](#anchor) and cross-file [text](path#anchor) link in localized files now points at the localized heading slug, computed with a faithful github-slugger implementation (lowercase, drop emoji/punctuation, whitespace → hyphens, preserve the leading hyphen produced by a leading emoji + space).
5. {#id} cleanup — the ja-jp draft used Pandoc-style explicit heading IDs that GitHub does not honor; these were stripped and the dependent anchors re-canonicalized.
6. TOC additions — the new 🌐 Use Your Preferred Language section is mirrored in every locale, and the top-of-page TOC strip includes a localized 🌐 [Your Language] entry pointing to that locale's section.

Verification

• A path verifier (MD_LINK + HTML_SRC + HTML_HREF regex resolution) reports 0 missing files and 0 broken relative paths across all 5 locales.
• The anchor fixer is idempotent — re-running it after the merge of any locale produces 0 additional changes.
• Spot-checked rendered TOC output in each locale; e.g. ko-kr root README now reads:

  🎯 학습 목표 ✅ 사전 요건 🤖 Copilot 제품군 📚 강의 구성 📋 명령어 참조 🌐 내 언어

Notes for reviewers

• Translations preserve heading structure and document order so future edits to the English source can be diffed positionally.
• Any future English content additions should follow the same pattern: add to the original first, then mirror into each localization/<locale>/... file at the same heading position.
• Cross-locale anchors (e.g. links from ko-kr/02-context-conversations to ko-kr/appendices/additional-context.md#…) are remapped to the target locale's heading slug, not the English slug.