[Docs] Update specification URL to `latest`

[koic]

Motivation and Context

This PR updates the specification URL to latest. This change avoids the need to update the URL whenever a new protocol version is released. The latest path redirects to the latest protocol version.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation update

Checklist

• [x] I have read the MCP Documentation
• [x] My code follows the repository's style guidelines
• [x] New and existing tests pass locally
• [x] I have added appropriate error handling
• [x] I have added or updated documentation as needed