ammo system

* heads have abilities
* health and ammo shows in ui

src/aim/target_ui.rs

@@ -1,7 +1,7 @@
 use super::AimState;
 use crate::{
     GameState,
-    backpack::BackpackHead,
+    backpack::UiHeadState,
     heads_ui::HeadsImages,
     loading_assets::UIAssets,
     npc::{Hitpoints, NpcHead},
@@ -18,7 +18,7 @@ struct HeadDamage;
 
 #[derive(Resource, Default, PartialEq)]
 struct TargetUi {
-    head: Option<BackpackHead>,
+    head: Option<UiHeadState>,
 }
 
 pub fn plugin(app: &mut App) {
@@ -150,7 +150,7 @@ fn sync(
     let mut new_state = None;
     if let Some(e) = aim.target {
         if let Ok((hp, head)) = target_data.get(e) {
-            new_state = Some(BackpackHead {
+            new_state = Some(UiHeadState {
                 head: head.0,
                 health: hp.health(),
                 ammo: 1.,