Native support for xAI Grok3

Model shorthand mapping related fixes
Comprehensive auto-mode related tests

README.md

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 https://github.com/user-attachments/assets/8097e18e-b926-4d8b-ba14-a979e4c58bda
 
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-  <b>🤖 Claude + [Gemini / O3 / OpenRouter / Ollama / Any Model] = Your Ultimate AI Development Team</b>
+  <b>🤖 Claude + [Gemini / O3 / GROK / OpenRouter / Ollama / Any Model] = Your Ultimate AI Development Team</b>
 </div>
 
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 **Option B: Native APIs**
 - **Gemini**: Visit [Google AI Studio](https://makersuite.google.com/app/apikey) and generate an API key. For best results with Gemini 2.5 Pro, use a paid API key as the free tier has limited access to the latest models.
 - **OpenAI**: Visit [OpenAI Platform](https://platform.openai.com/api-keys) to get an API key for O3 model access.
+- **X.AI**: Visit [X.AI Console](https://console.x.ai/) to get an API key for GROK model access.
 
 **Option C: Custom API Endpoints (Local models like Ollama, vLLM)**
 [Please see the setup guide](docs/custom_models.md#option-2-custom-api-setup-ollama-vllm-etc). With a custom API you can use: