Add deepseek-v4-flash / deepseek-v4-pro model support

Is your feature request related to a problem? Please describe.

No

Describe the solution you'd like

When I use aichat and "No config file, create a new one", the model listed under deepseek are deepseek-chat and deepseek-reasoner, which will be deprecated soon(according to https://api-docs.deepseek.com/), but no deepseek-v4-flash / deepseek-v4-pro to choice.