feat(i18n): add Japanese translation

[shuuji3]

fix #271

initial Japanese translation!

notes: I kept 'issues' and 'Organization' untranslated as it is proper nouns in github

ref.

• https://docs.github.com/ja/issues
• https://docs.github.com/ja/organizations

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Project	Deployment	Review	Updated (UTC)
docs.npmx.dev	Ready	Preview, Comment	Jan 29, 2026 11:02am
npmx.dev	Ready	Preview, Comment	Jan 29, 2026 11:02am

1 Skipped Deployment

Project	Deployment	Review	Updated (UTC)
npmx-lunaria	Ignored		Jan 29, 2026 11:02am

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[shuuji3]

It looks like autofix bot removed the EOF newlines 😄

[shuuji3]

Thank you!