Is your feature request related to a problem? Please describe.

If the configuration directory of VitePress is outside the project root directory, the project will not run correctly, so add this validation logic to ensure that the path entered by the user is within the root directory.

Describe the solution you'd like

I'd like to complete @yyx990803 remaining TODO code and achieve the purpose of prompting users to "Make sure directory is inside.".

And the pull request (#3640) is the solution for this issue.

Describe alternatives you've considered

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the docs.
• Read the Contributing Guidelines.
• Check that there isn't already an issue that asks for the same feature to avoid creating a duplicate.