OpenAI Chat Completions

入口：POST /v1/chat/completions

网关支持 OpenAI Chat Completions 请求和 streaming，但模型是否可以通过该入口调用，必须以公开兼容矩阵和客户 workspace 授权为准。

curl "${AI_GATEWAY_BASE_URL}/v1/chat/completions" \
  -H "Authorization: Bearer ${AI_GATEWAY_API_KEY}" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "<model-id-from-approved-catalog>",
    "messages": [{"role": "user", "content": "Review this change"}],
    "max_tokens": 256
  }'