Voice input fails with OpenAI models in ADK web

[Softdev1]

Description

The microphone feature throws "Unsupported post type for OpenAI connection" error when attempting to use voice input with OpenAI models. Feature currently only works with Gemini models.

Definition of Done

• Voice input works with OpenAI models without errors
• Voice input continues to work with Gemini models (no regression)
• Error handling displays user-friendly messages for unsupported models