Add support for DeepSeek (OpenAI compatible, endpoint configuration)

[muzzwood]

ChatGPT for example isn't available everywhere. In Hong Kong we can't use it without a VPN.
Having DeepSeek (or another more widely available LLM) as an option would be nifty 😃

Here's a community PHP SDK for it: https://github.com/deepseek-php/deepseek-php-client

[Mark-H]

It's compatible with OpenAI so should just be a matter of changing the base endpoint. It's a little light on configuration atm but that's definitely one of the things to add soon.

https://github.com/modmore/AIKit/blob/main/core/components/aikit/src/LLM/Models/OpenAI.php#L48