i18n(ja): Update frontmatter.md

[morinokami]

What kind of changes does this PR include?

• Changes or translations of Starlight docs site content

Description

• Update frontmatter.md.
  • Define the order of links in sidebar #359
  • Add support for customising sidebar labels from frontmatter #424

[changeset-bot]

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Latest commit: 505984d

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[delucis]

And we’re up-to-date! Great work @morinokami 🙌