Add custom base url from env

[clem844]

Add custom base url for deepagents-cli

[eyurtsev]

I don't want to introduce more env variables for this. We'll add a configuration file

[flingjie]

I don't want to introduce more env variables for this. We'll add a configuration file

In deepagents-cli, the create_model method was implemented in place of init_chat_model from langchain.chat_models. Could you share the key differences in the approach, and how do you see this change potentially improving flexibility, scalability, or performance in the future?