fix: update Japanese translation for document link in plugin.ts, translation for "endpointsDocLink" label

[t-daisuke]

Summary

Refined the Japanese translation for the endpointsDocLink label to improve clarity and naturalness.

Previously:

• endpointsDocLink: 'エンドポイントのドキュメント'

This translation was technically correct, but slightly awkward in a user-facing context. The updated version uses a clearer and more actionable phrase.

Updated to:

• endpointsDocLink: 'ドキュメントを表示する' ("View documentation")

This wording better reflects a typical UI label or button action, aligning with standard Japanese UX writing.

Screenshots

Before	After
エンドポイントのドキュメント	ドキュメントを表示する

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[crazywoola]

Thanks for the contribution :)

If you have more findings, please merge those into one PR. :)