feat: add deepseek translation service

[AkimioJR]

No description provided.

[windingwind]

thanks.

any reason not to reuse the logic of chatgpt.ts?

and please update the readme

[AkimioJR]

Although DeepSeek currently uses the OpenAI format for data transmission, it is a distinct AI service provider from ChatGPT. In the future, DeepSeek may cease using the OpenAI format for transmission, or alternatively, chatgpt.ts should be renamed to openai.ts

[cislunarspace]

I have tested using DeepSeek's API to fulfill the translation service and add support for the thinking-level feature. Please refer to PR 1464.

Currently, the API can be accessed via the base URL https://api.deepseek.com/chat/completions. However, when configuring it in coding applications, we typically just input https://api.deepseek.com instead of the full endpoint. I hope that in the future, we could add support for the base URL styles commonly used by Chat Completion, Responses, and Anthropic APIs.

@AkimioJR @windingwind