chore: Update docs for supported messaged roles

[louis-jan]

Cortex version

latest

Describe the issue and expected behaviour

Minor: there are 3 supported message roles at the moment:

• system (later developer?)
• user
• assistant

Steps to Reproduce

Go to cortex.so, click API reference, see Create Message section

Screenshots / Logs

What is your OS?

• Windows
• Mac Silicon
• Mac Intel
• Linux / Ubuntu

What engine are you running?

• cortex.llamacpp (default)
• cortex.tensorrt-llm (Nvidia GPUs)
• cortex.onnx (NPUs, DirectML)

Hardware Specs eg OS version, GPU

No response

[namchuai]

@louis-jan , we are following OpenAI's documentation. https://platform.openai.com/docs/api-reference/messages/createMessage

When storing messages, we only accept user or assistant role. system will be used in /chat/completion API, but not for /messages API.