Clarify that footer is hidden on custom mode pages

[mintlify]

Summary

• Updated the custom page mode documentation to clarify that the footer is hidden along with the sidebar and table of contents
• This reflects the frontend behavior change from mintlify/mint#6393
• Updated English, French, Spanish, and Chinese translations

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Note

Low Risk
Documentation-only updates that clarify page layout behavior and adjust localized punctuation; no runtime code changes.

Overview
Clarifies the custom page mode documentation to explicitly state that the footer is hidden along with the sidebar and table of contents (English, Spanish, Chinese, and French).

Also normalizes French typography (apostrophes/punctuation) and fixes a missing trailing newline in fr/editor/pages.mdx.

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