GoogleProviderHandler:
- Wrap validated response dict in JSONResponse before returning
- Add logging to confirm JSONResponse is being returned
- Ensures proper JSON serialization for Google GenAI responses

AnthropicProviderHandler:
- Wrap validated response dict in JSONResponse before returning
- Add logging to confirm JSONResponse is being returned
- Ensures proper JSON serialization for Anthropic responses

RequestHandler:
- Remove JSONResponse wrapping (now handled by providers)
- Update logging to detect JSONResponse vs dict responses
- OpenAI and Ollama providers return raw dicts (already compatible)

This fixes client-side 'Cannot read properties of undefined' errors by ensuring
Google and Anthropic responses are properly serialized as JSONResponse,
while leaving OpenAI and Ollama responses as-is since they're already
OpenAI-compatible.