docs: Update Korean translation for 'Usage with NextJS' document

[Gaic4o]

Background

The "Usage with NextJS" document has been updated.

• Improved clarity and readability in the translation:
  • Standardized terminology (consistently using "폴더" instead of mixing "디렉토리" and "폴더")
  • Overall, we have improved the sentences to be more understandable by using accurate terminology.

[Copilot]

Pull Request Overview

This PR updates the Korean translation for the "Usage with NextJS" document to improve clarity and consistency in terminology. Key changes include:

• Standardizing terminology (e.g. using "폴더" consistently)
• Revising section headings and descriptions for clearer explanation of NextJS's routing and FSD architecture
• Updating folder structure descriptions to enhance readability

Comments suppressed due to low confidence (1)

i18n/kr/docusaurus-plugin-content-docs/current/guides/tech/with-nextjs.mdx:13

• [nitpick] Consider using consistent terminology for the layer terminology ('pages layer' vs. '페이지 레이어') throughout the document to ensure clarity for all readers.

## FSD와 NextJS의 `pages` layer 충돌 {#pages-conflict}