spicetify/cli ? reverse-engineered prompt

Build me a command-line tool that lets me customize the official Spotify desktop client. I want to be able to take control of its appearance and functionality.

The main feature should be theming. It should let me change the color scheme across the entire UI and apply custom styles using CSS to get the exact look I want. I should be able to make Spotify look completely different from the default.

It should also support extensions or plugins, probably using JavaScript, to add new features that Spotify doesn't have. For example, manipulating the UI, extending the player's capabilities, or adding entirely new panels. Let's also add support for injecting full "custom apps" into the client.

This has to be a CLI tool, and it's important that it works across Windows, macOS, and Linux. It's all about making the Spotify client my own.