Allow custom deepseek self-hosted URL

[chsasank]

I'd like to use my own custom self hosted deepseek model instance as opposed to sending my data to Chinese servers. I think we can do this quite easily by configuring the deepseek base url.

Relevant code line:
https://github.com/getAsterisk/deepclaude/blob/ebf8d369abcd2f4b9056d4857ca2ef7980537749/src/clients/deepseek.rs#L68C44-L68C85

How can we expose this via configuration? Any ideas, happy to send in a PR if you give me a plan to implement.

[stan1233]

Great idea! Could you also handle the custom ANTHROPIC self-hosted URL while you're at it?