Document default property for version navigation

[mintlify]

Summary

• Adds documentation for the default boolean property on version objects
• Explains that by default the first version in the array is used
• Includes code example showing how to set a different default version

Replaces #4309 (English only as requested).

---

Note

Low Risk
Low risk documentation-only change that clarifies how the default version is chosen in versioned navigation.

Overview
Adds documentation for selecting a default version in navigation.versions, clarifying that the first entry is used unless a version object sets default: true.

Updates the docs.json settings reference to include the default boolean on version entries and describes its behavior alongside existing tag documentation.

^{Written by Cursor Bugbot for commit 48fe18e. This will update automatically on new commits. Configure here.}

[ethanpalm]

lgtm! just a few small edits to use the word "default" a bit less 😄

[ethanpalm]

fine to ignore the failing test. It's been flaky all day but the preview looks good and nothing in this PR should possibly break anything