Add Copy for LLM button to component pages

[jmrada14]

Summary

• Adds a "Copy for LLM" button to component documentation pages, next to
  the Code/Design buttons
• Button copies the full component documentation (all tabs: examples,
  usage, accessibility) as clean markdown to the clipboard
• Includes inline code examples from LivePreview components
• API route reads MDX source files from disk, strips JSX/frontmatter, and
  returns clean markdown

Test plan

• Navigate to a component page (e.g., /salt/components/button/usage)
• Verify the "Copy for LLM" button appears next to the Code button in
  the heading
• Click the button and paste into a text editor — verify clean markdown
  with title, description, examples, usage, and accessibility content
• Verify the button does NOT appear on pattern, foundation, or other
  non-component pages

[changeset-bot]

⚠️ No Changeset found

Latest commit: 90dd53a

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[jmrada14]

Changeset does not list docs site.

PR for issue: #6024