docs: Add complete setup guide for common LLM providers

[0xallam]

We need to add a comprehensive setup guide that covers how to configure Strix with the most popular LLM providers.

The doc should include:

• OpenAI (GPT-5.1, codex, etc.)
• Anthropic (Claude Sonnet / Opus)
• Google (Gemini)
• Azure OpenAI
• DeepSeek / Groq
• OpenRouter
• Ollama
• LMStudio
• etc..

Each provider section should include:

• Required API keys / environment variables
• Example litellm config
• Recommended model(s) for best Strix performance
• Common pitfalls + troubleshooting

[yokoszn]

wip : https://github.com/TWN-Systems/strix-docs will submit a PR later tonight

[amille44420]

I myself have been using AWS Bedrock for Cloud provider with Anthropic models. I noticed it wasn't there ? There are some issues but overall it still seems to be able to work things out. However I noticed I have to set whatever value to LLM_API_KEY as it's mandatory by strix though actually not needed as I have an authenticated environment to run strix.