[DevTools] Document react-devtools-cdt-mcp for npm consumers (#37503)

## Summary
- Rewrite the package README so npm consumers can tell this is a
page-side library, not an MCP server.
- Document the chrome-devtools-mcp 1.3.0+ requirement, the experimental
third-party flag, and the corrected DOM-tool output.

Stacked on https://github.com/react/react/pull/37497

## Test plan
- [ ] Read the README as a first-time installer and confirm install,
import order, and MCP config are clear.
- [ ] Confirm `react_get_component_by_dom_element` no longer documents
`hooks`.