[bug]admin页面添加模型无法设置最大输出长度，导致使用时最大只能到4096

**Describe the bug**

admin页面添加模型无法设置最大输出长度，导致使用时最大只能到4096
**To Reproduce**

Steps to reproduce the behavior:
1. 登录coze-studio平台
2. 访问admin页面
3. 添加模型

可以看到没有设置最大输出长度的选项

5. 在智能体页面选用添加的模型

模型最大长度只有4096

**Expected behavior**

模型可以设置最大长度

**Screenshots**

**Version:**
0.5.0

**Environment:**

The output of `go env`.

**Additional context**

Add any other context about the problem here.

Start at the admin page's add-model flow described in the reproduction steps and trace how the model settings are presented and saved. Add a maximum output length setting that is available for the model and verify in the agent page that the configured value is reflected instead of being capped at 4096.

Written by the indexing model from the issue text.