docs: Add Google ADK integration guide

[VIKAS9793]

Adds documentation for integrating A2UI with Google Agent Development Kit (ADK).

Includes:

• Architecture overview (protocol bridge pattern)
• Complete bridge server code (Python/FastAPI)
• A2UI configuration steps
• Windows compatibility notes
• Troubleshooting guide

Based on real-world integration experience with AI Technical Interviewer project.

Related: Discussion #390