Add page Markdown and prompt copy actions to the Ask AI menu

## Feature request

Add two copy actions to the existing Ask AI menu. These actions let users use the page content in any AI tool.

### Copy this page Markdown

Add a **Copy this page Markdown** action. Get the source Markdown or MDX file from GitHub and copy its content.

The copied content must match the source for the current documentation page.

### Copy prompt text

Add a **Copy prompt text** action. Copy a standard prompt that refers to the current page.

Use a prompt similar to the prompt in the current ChatGPT and Claude actions. Include the page title and URL.

Example:

```text
Read this Babylon documentation page and help me understand it:
```

## Acceptance criteria

- The Ask AI menu contains both copy actions.
- The Markdown action gets the correct source file from GitHub.
- The Markdown action copies the complete source without rendered HTML.
- The prompt action copies a standard prompt with the current page title and URL.
- The interface shows a clear success or error message after each copy action.
- Users can operate both actions with a keyboard and a screen reader.

Start by locating the existing Ask AI menu and its ChatGPT and Claude actions. Trace how the current documentation page title, URL, and GitHub source Markdown or MDX file are identified, then follow the existing copy feedback behavior. Done means both actions copy the specified content, expose clear success or error feedback, and work with keyboard and screen-reader input.

Written by the indexing model from the issue text.