Add native Markdown preview in the Codex macOS app

Hey @AndresTheDesigner, thanks for bringing this to our attention. A couple quick questions so we can pass along the right details:

1. What are you ultimately trying to accomplish, in your own words?

2. What do you do today instead, and what about that isn’t working for you?

3. If we solved this perfectly, what would be different for you or your team?

Appreciate any extra details you can share. They’ll help us reproduce it and get it in front of the right folks.