use gamestates and assetloader

src/backpack/mod.rs

@@ -1,6 +1,6 @@
 mod backpack_ui;
 
-use crate::heads_ui::HEAD_COUNT;
+use crate::{GameState, heads_ui::HEAD_COUNT};
 use bevy::prelude::*;
 
 pub use backpack_ui::BackpackAction;
@@ -28,7 +28,7 @@ pub struct BackbackSwapEvent(pub usize);
 pub fn plugin(app: &mut App) {
     app.add_plugins(backpack_ui::plugin);
 
-    app.add_systems(Startup, setup);
+    app.add_systems(OnEnter(GameState::Playing), setup);
 }
 
 fn setup(mut commands: Commands) {