[Bug] Authentication Fails in NextChat + One-API Local Deployment When Using DeepSeek Official Model & API

### 📦 Deployment Method

Docker

### 📌 Version

2.6.0

### 💻 Operating System

Windows

### 📌 System Version

win10

### 🌐 Browser

Chrome

### 📌 Browser Version

Latest

### 🐛 Bug Description

When deploying NextChat with One-API locally, an "Authentication Fails (no such user)" error occurs when attempting to use the DeepSeek official model. The issue arises because NextChat does not correctly route requests through One-API's gateway, instead attempting to directly call DeepSeek's API without using the One-API Token. Other UI applications (e.g., Chatbox) work correctly with the same setup.

Error Message:
```

JSON
{
"error": {
"message": "Authentication Fails (no such user)",
"type": "authentication_error",
"param": null,
"code": "invalid_request_error"
}
}
```

### 📷 Recurrence Steps

1. Deploy NextChat and One-API locally.
2. Add DeepSeek's API key and other channels (e.g., Alibaba's Tongyi Qianwen) in One-API.
3. Configure NextChat's environment variables with the One-API token as follows:
environment:
- OPENAI_API_KEY=sk-dUJhlhHAabdVXsqN22B205Bxxxxxxxxxxxxx6e65B1Ad
- CODE=xxxxx
- BASE_URL=http://154.xxx.241.166:3000
- CUSTOM_MODELS=-all,+deepseek-ai/DeepSeek-R1,+Pro/deepseek-ai/DeepSeek-R1,+deepseek-ai/DeepSeek-V3,+Pro/deepseek-ai/DeepSeek-V3,+deepseek-r1,+deepseek-v3,+qwen-max-latest,+deepseek-r1-250120,+deepseek-v3-241226,deepseek-chat,deepseek-reasoner
- DEFAULT_MODEL=deepseek-chat

### 🚦 Expected Behavior

NextChat should route requests through One-API's gateway and successfully connect to the DeepSeek model using the One-API Token.

Actual Behavior:
An "Authentication Fails (no such user)" error occurs. The logs indicate that NextChat is attempting to directly call DeepSeek's API without using the One-API Token.

### 📝 Additional Information

The issue is similar to a previously reported bug where NextChat failed to route requests correctly for the [SiliconFlow model](https://github.com/ChatGPTNextWeb/NextChat/issues/6286).
Other UI applications (e.g., Chatbox) work correctly with the same One-API setup, indicating that the issue is specific to NextChat's implementation.


Proposed Solution:

Ensure that NextChat correctly routes requests through One-API's gateway and uses the One-API Token for authentication.
Verify that the BASE_URL and OPENAI_API_KEY environment variables are correctly configured in NextChat.
Update NextChat's request handling logic to properly utilize One-API's gateway for all model requests.