Make themes work on Linux and Windows

[NetOpWibby]

The settings window is currently set to respond to commands on macOS. Relevant Rust code: src-tauri/src/main.rs.

Ideally, it'd be great to update that code to give Linux/Windows users the same capability. In the meantime, modifying the config file in your system's app config folder is the only way. Relevant SvelteKit code: src/App.svelte