bug: 升级到新版本后，自定义模型不可用了。cindy模型、codex订阅模型正常。

### 问题描述 / What happened

升级到新版本之后，自定义模型不可用了，返回：{"error":{"type":"invalid_request_error","code":"unsupported_feature","message":"Responses feature is not supported by the Chat Completions bridge: tools[3].web_search"}}。使用旧版本正常可用。

### 环境 / Environment

- Cindy 版本或 commit / version or commit:
- 平台与版本 / platform & OS version:
- 安装方式 / install method:

### 复现步骤 / Steps to reproduce

1. 选择自定义配置的模型（没有做任何变更、我另一台电脑的旧版本相同的模型配置可用）
2. 正常问答，返回：{"error":{"type":"invalid_request_error","code":"unsupported_feature","message":"Responses feature is not supported by the Chat Completions bridge: tools[3].web_search"}}
3. 升级到0.1.44版本和0.1.45版本都存在此问题

### 日志与截图 / Logs & screenshots

Start by reproducing the custom-model request on versions 0.1.44 and 0.1.45, then trace where the tools[3].web_search option is added and handled by the Chat Completions bridge. Done means custom models no longer return the unsupported_feature error while Cindy and Codex subscription models continue to work.

Written by the indexing model from the issue text.