Unable to run with free tier API key

### Description of the bug:

When using a free tier Gemini API Key generated from Google AI Studio, the server output following the example `python examples/cli_research.py "What are the latest trends in renewable energy?"` produces the below error:

```
Retrying langchain_google_genai.chat_models._chat_with_retry.._chat_with_retry in 2.0 seconds as it raised ResourceExhausted: 429 Gemini 2.5 Pro Preview doesn't have a free quota tier. For more information on this error, head to: https://ai.google.dev/gemini-api/docs/rate-limits. [violations {
quota_metric: "generativelanguage.googleapis.com/generate_content_free_tier_requests"
quota_id: "GenerateRequestsPerDayPerProjectPerModel-FreeTier"
quota_dimensions {
key: "model"
value: "gemini-2.5-pro-exp"
}
quota_dimensions {
key: "location"
value: "global"
}
}
...
```

### Actual vs expected behavior:
works

### Any other information you'd like to share?

_No response_