[Feature] Set a filetype for the claude-code buffer

## Feature Description

It would be convenient if this plugin set a filetype for the terminal that it opens

## Use Case

This makes it easier to target autocmds only to this specific window. E.g. I want to set `buflisted = false` for these, and this would make it possible without having to add more options to the plugin (though happy to add a `buflisted` option if you want)
