Clarify AI provider prompt types in contextual menu

[mintlify]

Summary

• Clarified that ChatGPT receives the plain page URL while Claude, Perplexity, Grok, Google AI Studio, Devin, and Windsurf receive the Markdown version of the page
• Added a new "How AI providers receive page content" section explaining the prompt type differences
• Updated the menu options table to distinguish between "URL as context" and "Markdown context"

Triggered by mintlify/mint@ee455fd

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Note

Low Risk
Low risk documentation-only change that updates wording and adds an explanatory section; no runtime behavior is modified.

Overview
Updates ai/contextual-menu.mdx to distinguish the context sent to each AI provider: ChatGPT uses the plain page URL, while Claude/Perplexity/Grok/AI Studio/Devin/Windsurf use the page’s Markdown (.md).

Adds a new How AI providers receive page content section explaining the URL-vs-Markdown behavior and links to the Markdown output docs.

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[brandonmcconnell]

None of this is really that helpful, and the only difference here is that ChatGPT can't currently read Markdown URLs. But hopefully that will change soon, and then these will all be aligned anyway, so I'm closing this PR.