Japanese Patterns Book - Ideas for further improvement

As part fo #422 we identified some things that are not essential for the first release of the Japanese Patterns Book.
Still they could be considered to improve the book further.

These ideas are listed below, and after the first book release we can decide how to prioritize these.

Future Work for the Japanese Patterns Book

• maintenance - The lint-patterns.yml GHA checks that all patterns contain the mandatory headlines as defined in .meta/pattern-template.md. This isn't essential for JP patterns, as those are translations of EN patterns anyways, for which we have confirmed that they have these mandatory headlines. We can try to adapt this GHA to also check the required headlines in JP patterns but it isn't essential
• ✅ structure/maintenance - I am suggesting to rename the folder translation/japanese to translation/ja to make it consistent with the book URL as well as the book/ja folder - see #452
• structure/maintenance - inside of translations/jp keep the same folder structure as in patterns (that way all links to other patterns and assets will stay the same). => As this would require to check all links in the JP patterns again I am pushing this to Future Work
• gitbook publishing - update book-jp branch automatically when changes to main are made. => I am opting to do this manually for now, as it does not require more than merging main into book-jp. In the future we can automate this, maybe with this action to create a PR and this one to auto-merge. or better to merge without a PR?
• content - what to do with the mindmap? book/explore-patterns.md - We decided to keep it in English for the 1st release
• content - the captions of most images are still in English e.g. see this
• ✅ content - translate the book cover itself to Japanese too? (I do have the source files, so if somebody helps me with the translations then we can do this)

今後の作業項目を1つ選び、参照されているエントリーポイントから始めます。メンテナンスについては .meta/pattern-template.md と lint-patterns.yml、構造については translation/japanese と translations/jp フォルダ、コンテンツについては book/explore-patterns.md を使用します。関連する issue のリンクを確認し、選択した改善が実装され、影響を受ける日本語版の書籍リンク、コンテンツ、または公開ワークフローが検証されたことを完了条件として定義します。