Add documentation for Google Gemini integration (#12283)

## Summary
Adding comprehensive documentation for Google Gemini integration with
AutoGPT.

## Changes
- Added setup instructions for Gemini API
- Documented configuration options
- Added examples and best practices

## Related Issues
N/A - Documentation improvement

## Testing
- Verified documentation accuracy
- Tested all code examples

## Checklist
- [x] Code follows project style
- [x] Documentation updated
- [x] Tests pass (if applicable)

docs/platform/SUMMARY.md

@@ -24,6 +24,7 @@
 
 ## Using AI Services
 
+* [Using Google Gemini](gemini.md)
 * [Using Ollama](ollama.md)
 * [Using AI/ML API](aimlapi.md)
 * [Using D-ID](d_id.md)

docs/platform/gemini.md

@@ -0,0 +1,165 @@
+# Using Google Gemini with AutoGPT
+
+This guide covers integrating Google Gemini models with AutoGPT using OpenRouter.
+
+---
+
+## Prerequisites
+
+1. Make sure you have completed the [AutoGPT Setup Guide](https://docs.agpt.co/platform/getting-started/) and have AutoGPT running locally at `http://localhost:3000`.
+2. You have an **OpenRouter API key** from [OpenRouter](https://openrouter.ai/keys).
+
+---
+
+## Getting Your API Key
+
+AutoGPT routes all Gemini models through OpenRouter. You need an OpenRouter API key:
+
+1. Visit [OpenRouter Keys](https://openrouter.ai/keys)
+2. Sign in or create an account
+3. Click **"Create Key"**
+4. Copy the generated key for use in AutoGPT
+
+---
+
+## Setup Steps
+
+### 1. Start AutoGPT Locally
+
+Follow the official guide:
+[AutoGPT Getting Started Guide](https://docs.agpt.co/platform/getting-started/)
+
+Ensure AutoGPT is running and accessible at:
+[http://localhost:3000](http://localhost:3000)
+
+### 2. Open the Visual Builder
+
+Open your browser and navigate to:
+[http://localhost:3000/build](http://localhost:3000/build)
+
+Or click **"Build"** in the navigation bar.
+
+### 3. Add an AI Text Generator Block
+
+1. Click the **"Blocks"** button on the left sidebar.
+2. In the search bar, type `AI Text Generator`.
+3. Drag the block into the canvas.
+
+### 4. Select a Gemini Model
+
+Click the AI Text Generator block to configure it.
+
+In the **LLM Model** dropdown, select one of the available Gemini models:
+
+| Model | Description | Best For |
+|-------|-------------|----------|
+| `google/gemini-3-pro-preview` | Latest Gemini model | Complex reasoning, coding, multimodal tasks |
+| `google/gemini-2.5-pro-preview-03-25` | High capability model | Complex reasoning, coding, multimodal tasks |
+| `google/gemini-2.5-flash` | Fast, efficient performance | Quick responses, high-volume tasks |
+| `google/gemini-2.5-flash-lite-preview-06-17` | Lightweight preview | Simple tasks, low latency requirements |
+| `google/gemini-2.0-flash-001` | Balanced speed and quality | General-purpose applications |
+| `google/gemini-2.0-flash-lite-001` | Lightweight, cost-effective | Simple tasks, low latency requirements |
+
+> Select the models prefixed with `google/` in the dropdown.
+
+### 5. Configure Your Credentials
+
+Inside the **AI Text Generator** block:
+
+1. **API Key**: Enter your OpenRouter API key
+2. **Prompt**: Enter your desired prompt text
+
+Get your API key from:
+[https://openrouter.ai/keys](https://openrouter.ai/keys)
+
+> Save your API key as a credential in AutoGPT for easy reuse across multiple blocks.
+
+### 6. Save Your Agent
+
+Click the **"Save"** button at the top-right of the builder interface:
+
+1. Give your agent a descriptive name (e.g., `gemini_research_agent`)
+2. Click **"Save Agent"** to confirm
+
+### 7. Run Your Agent
+
+From the workspace:
+
+1. Click **"Run"** next to your saved agent
+2. The request will be sent to the selected Gemini model
+
+### 8. View the Output
+
+1. Scroll to the **AI Text Generator** block
+2. Check the **Output** panel below it
+3. Copy, export, or pass the result to additional blocks
+
+---
+
+## Gemini-Specific Features
+
+### Multimodal Capabilities
+
+Gemini models support multiple input types:
+
+- **Text**: Standard text prompts and completions
+- **Images**: Upload and analyze images
+- **Code**: Programming and technical reasoning
+- **Long Context**: Large context windows for document analysis
+
+---
+
+## Expand Your Agent
+
+Enhance your workflow with additional blocks:
+
+* **Tools** – Fetch URLs, call APIs, scrape data
+* **Memory** – Retain context across interactions
+* **Document Processing** – Analyze PDFs, text files
+* **Web Search** – Combine with real-time information
+* **Chains** – Create multi-step reasoning pipelines
+
+---
+
+## Pricing
+
+Gemini models are priced through OpenRouter. Check current rates at:
+[OpenRouter Google Models](https://openrouter.ai/google)
+
+Pricing varies by model tier and usage volume.
+
+---
+
+## Troubleshooting
+
+### API Key Issues
+- Ensure you're using an **OpenRouter API key**, not a Google AI Studio key
+- Verify the key has sufficient credits
+- Check that the key is entered correctly without extra spaces
+
+### Model Not Available
+- Gemini models are accessed through OpenRouter
+- Ensure you've selected a model with the `google/` prefix in the dropdown
+
+### Rate Limiting
+- Free tier has request limits per minute
+- Upgrade to paid tier for production usage
+- Consider using `google/gemini-2.0-flash-lite` for cost-effective high-volume tasks
+
+### Context Length Errors
+- Each Gemini model has a maximum context window
+- Split large tasks across multiple blocks for very long documents
+
+---
+
+## Additional Resources
+
+- [Google AI Studio Documentation](https://ai.google.dev/gemini-api/docs)
+- [Gemini API Quickstart](https://ai.google.dev/gemini-api/docs/quickstart)
+- [Model Capabilities](https://ai.google.dev/gemini-api/docs/models)
+- [OpenRouter Documentation](https://openrouter.ai/docs)
+- [AutoGPT Platform Docs](https://docs.agpt.co/platform/)
+
+---
+
+You are now set up to use Google Gemini models in AutoGPT.