docs(cua-driver): add integration chooser

[f-trycua]

Summary

• add one integration chooser for MCP, same-process SDK, private workers, and app-hosted services
• explain runtime-owned permissions, private MCP transport lifecycles, and public session labels
• explain why Cua Driver can attach to an approved existing browser without the restart required by launch-flag-only CDP tools
• surface the chooser from the docs home, Concepts, installation, agent connection guide, and first-app tutorial

Why

The individual setup and reference pages exist, but integrators do not have one simple starting point that tells them which surface fits their architecture.

Validation

• docs/node_modules/.bin/tsx scripts/check-links.ts
• docs/node_modules/.bin/tsx scripts/check-hygiene.ts
• docs/node_modules/.bin/next build
• rendered the new route in an isolated Chrome instance through Cua Driver with an exact process/tab binding; verified the navigation entry, layout, decision table, and linked installation route

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