[Feature]: add a way to use MiniMax as provider

[whitelilis]

Prerequisites

• I will write this issue in English (see our Language Policy)
• I have searched existing issues and discussions to avoid duplicates
• This feature request is specific to oh-my-opencode (not OpenCode core)
• I have read the documentation

Problem Description

As a user who has subscribe of MiniMax, I want to use its api, but when install there is no way.
Opencode itself can set model of MiniMax manually, but how to config it in oh-my-opencode?

Proposed Solution

Add some configure for MiniMax and other third party provider, many provider use the OpenAI or Claude compact API.

Alternatives Considered

No response

Doctor Output (Optional)

Additional Context

No response

Feature Type

New Agent

Contribution

• I'm willing to submit a PR for this feature
• I can help with testing
• I can help with documentation

[jayjunjieqiu]

Here is a way to retrieve internal provider/model ID:
Use command opencode models
For the detailed configuration, refer to https://github.com/code-yeongyu/oh-my-opencode/blob/dev/docs/configurations.md.