Update theme to use the json format in Files v3.4

@weeebdev thank you for maintaining this theme for Files.

It seems that this popular theme relies on the previous theming system, which Files no longer supports. Since version 2.5, the theme system has changed, and now themes are saved directly within the settings file.

I'm attaching a link to the updated documentation https://files.community/docs/customize-settings/appearance.

You can also refer to https://github.com/catppuccin/windows-files which has an example of how to apply themes using PowerShell.

Regards,
Yair