chore: cmux natively supports opencode and omo

[fvnky07]

https://cmux.com/docs/agent-integrations/oh-my-opencode

I realise not everyone is using oh my openagents with cmux but i think the core functionality of this plugin has now become redundant.

thoughts?

[0xCaso]

@fvnky07 i think it makes sense to just remove opencode-cmux if you're using oh-my-opencode? if it's doing the same thing