Fix opencode command for kitty provider

[phantomwhale]

Kitty requires the executable and any extra arguments to be provided as an array of values. Before this change it would try and execute "opencode --port" and state no such executable could be found

This fixes the issue for the kitty provider; unsure if other providers would need a similar fix

[phantomwhale]

Whilst I'm here, I've also used this change to let me add --copy-env to my provider config (e.g. cmd = "--copy env opencode --port") which means kitty opens up the opencode subshell with the current environment; without that, opencode can't run my test suites etc... as it doesn't have the right executables on it's PATH

Not sure if that would be something that should be part of this plugin by default, or if it's something deliberately left as an opt-it thing. Without this PR, I've simply not been able to do it at all (aside from hacking the option into my local copy of the kitty provider) hence I thought to raise it here as an FYI.

[NickvanDyke]

Whilst I'm here, I've also used this change to let me add --copy-env to my provider config (e.g. cmd = "--copy env opencode --port") which means kitty opens up the opencode subshell with the current environment; without that, opencode can't run my test suites etc... as it doesn't have the right executables on it's PATH

Oh neat, maybe that's the correct fix for #106 ?