Update links in quickstart.mdx to use .mdx extension

[michael-fp]

Fixed some of the links by adding the .mdx extension

Motivation and Context

The links at the bottom of the quickstart docs weren't correct.

How Has This Been Tested?

Manually tested each link.

Breaking Changes

No.

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)
• Documentation update

Checklist

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

Additional context

No additional context :)

[rdimitrov]

Thanks for the contribution! Unfortunately this change would break these links on the live documentation site.

This docs/modelcontextprotocol-io/ folder is published to https://modelcontextprotocol.io (via Mintlify), which uses extensionless routing for pages. I verified this directly:

• https://modelcontextprotocol.io/registry/package-types → 200
• https://modelcontextprotocol.io/registry/package-types.mdx → 404
• https://modelcontextprotocol.io/registry/authentication → 200
• https://modelcontextprotocol.io/registry/authentication.mdx → 404
• https://modelcontextprotocol.io/registry/github-actions.mdx → 404
• https://modelcontextprotocol.io/registry/remote-servers.mdx → 404

So while adding .mdx makes the links clickable when browsing the raw file on GitHub, it breaks the same links once rendered on the actual docs site, which is the canonical place these files are published to. Closing for now — happy to revisit if there's a different way to solve the GitHub-preview readability issue without affecting the live site. Thanks again for looking into this!