Editor smart substitution

[ethanpalm]

Documentation changes

This PR adds a table of smart substitution shortcuts in the editor.

Closes https://linear.app/mintlify/issue/DOC-274/document-typography-keyboard-shortcuts-in-the-editor

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For Reviewers

When reviewing documentation PRs, please consider:

✅ Technical accuracy

• Code examples work as written
• Commands and configurations are correct
• Links resolve to the right destinations
• Prerequisites and requirements are accurate

✅ Clarity and completeness

• Instructions are clear and easy to follow
• Steps are in logical order
• Nothing important is missing
• Examples help illustrate the concepts

✅ User experience

• A new user could follow these docs successfully
• Common gotchas or edge cases are addressed
• Error messages or troubleshooting guidance is helpful

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Note

Low Risk
Documentation-only changes plus a small Vale dictionary update; no runtime behavior or security-sensitive logic is modified.

Overview
Adds a new Smart substitutions section to editor/keyboard-shortcuts.mdx, documenting the character sequences the editor auto-converts (e.g., -> →, != ≠) and noting substitutions are skipped in inline/code blocks.

Also tweaks the Visual mode link shortcut wording and updates the Vale accepted vocabulary to allow outdent (case-insensitive) to avoid lint failures.

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