Use opencode.nvim instead of a seperate tmux window

[Luquatic]

Hi @dhh, I noticed in your recent merged pull requests that you added the nic() function that opens a tmux terminal split with nvim, opencode and a terminal. However there is this nvim plugin that integrades opencode in your project while also adding extra commands etc.

https://github.com/nickjvandyke/opencode.nvim?tab=readme-ov-file#opencodenvim

[pomartel]

The function is meant to be flexible. For example, there is also the nicx command that opens Claude Code instead. And the nic function opens the user preferred editor which might not be neovim.