AI ingestion page improvements

[ethanpalm]

This PR updates the https://mintlify.com/docs/ai-ingestion

Summary of changes:

• Move contextual menu to the top to increase discovery
• Add info on enabling the contextual menu to this page so people don't have to search for it
• Add screenshot to help people understand what the contextual menu is
• Combine Command + C and .md sections into a "Generating Markdown versions of pages" section since they are two ways to do the same thing
• Add a bit more conceptual info to each section about how these features help people engage with AI tools

❓ I cannot get the copy button in the contextual menu or the Command + C shortcut to successfully copy a page as Markdown. Is this a known bug or something local?
Edit: this was a Safari problem

[baell]

lgtm!