Document delete confirmation and wrap with sections

[mintlify]

Summary

• Added documentation for the new 'Wrap with' section in the root-level add dropdown that wraps existing content under a new division
• Added note about the confirmation dialog that now appears when deleting divisions or groups with children

Related to: mintlify/mint#6461

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Note

Low Risk
Documentation-only updates with no runtime or behavioral changes; risk is limited to potential wording/accuracy issues.

Overview
Updates editor/navigation.mdx to document the root-level Add new dropdown’s new Wrap with section (wrapping existing navigation under a new division) alongside the existing Add section.

Adds a note that deleting a division or group with children now triggers a confirmation dialog to prevent accidental deletion.

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