Rename machine button spawner, "big red button"

It's the big red button. Don't press it.

Or do.

src/widgets/mod.rs

@@ -57,7 +57,7 @@ fn machine_ui_base(header: impl Into<String>) -> impl Bundle {
 }
 
 // TODO: Hook up action handling (callback? Observer? Some other weird component?)
-fn spawn_machine_button(commands: &mut ChildSpawnerCommands, text: impl Into<String>) {
+fn spawn_big_red_button(commands: &mut ChildSpawnerCommands, text: impl Into<String>) {
   let mut builder = commands.spawn((
     Button,
     Node {