claude-code-router如何接入Gemini Balance？具体如何配置？ 

目前对于claude-code-router的模型供应商配置这块 
  "Providers": [    {
      "name": "gemini",
      "api_base_url": "https://xxx.com",
      "api_key": "sk-",
      "models": ["gemini-2.5-flash", "gemini-2.5-pro"],
      "transformer": {
        "use": ["gemini"]
      }
]

http://xxx.com Gemini Balance地址，对api_base_url参数尝试了以下配置 
http://xxx.com
http://xxx.com/v1/cha...