Add spellcheck to Vale vocabulary

[mintlify]

Adds spellcheck to the Vale vocabulary to prevent false positives from PR #4352 which introduced the term in editor/pages.mdx.

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Note

Low Risk
Low risk: a single documentation-lint configuration update that only affects Vale spellchecking outcomes.

Overview
Updates Vale’s Mintlify accepted vocabulary to include case-insensitive spellcheck, preventing the term from being flagged as a spelling/style error in docs.

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