refactor: fix bugs and improve architecture

- Fix double-execution bug in LevelStateHandler (coins/skills were committed twice per level)
- Fix DamageComponent to track multiple targets via HashSet instead of single node
- Fix HealthComponent: update health immediately, decouple from PlayerController via signal wiring in PlayerController
- Remove dead loop in SkillManager.RemoveSkill; simplify O(n²) throw skill loop
- Replace GetNode<T>(path) with .Instance across managers; add Instance to StatisticsManager/SpeedRunManager
- GameManager.GetPlayer() now uses EventBus.PlayerSpawned instead of scanning all scene nodes
- UIManager.UiStack: remove [Export], use private List<Control>
- PlayerState: extract DefaultLives constant, simplify CreateDefault()

Autoloads/UIManager.cs

@@ -1,11 +1,10 @@
 using Godot;
-using Godot.Collections;
 
 namespace Mr.BrickAdventures.Autoloads;
 
 public partial class UIManager : Node
 {
-    [Export] public Array<Control> UiStack { get; set; } = new();
+    private readonly System.Collections.Generic.List<Control> UiStack = new();
     
     [Signal] public delegate void ScreenPushedEventHandler(Control screen);
     [Signal] public delegate void ScreenPoppedEventHandler(Control screen);
@@ -34,19 +33,19 @@ public partial class UIManager : Node
             return;
         }
         
-        var top = (Control)UiStack[^1];
+        var top = UiStack[^1];
         UiStack.RemoveAt(UiStack.Count - 1);
         top.Hide();
         top.SetProcessInput(false);
         EmitSignalScreenPopped(top);
         top.AcceptEvent();
 
-        if (UiStack.Count > 0) ((Control)UiStack[^1]).GrabFocus();
+        if (UiStack.Count > 0) UiStack[^1].GrabFocus();
     }
     
-    public Control TopScreen() => UiStack.Count > 0 ? (Control)UiStack[^1] : null;
-    
-    public bool IsScreenOnTop(Control screen) => UiStack.Count > 0 && (Control)UiStack[^1] == screen;
+    public Control TopScreen() => UiStack.Count > 0 ? UiStack[^1] : null;
+
+    public bool IsScreenOnTop(Control screen) => UiStack.Count > 0 && UiStack[^1] == screen;
     
     public bool IsVisibleOnStack(Control screen) => UiStack.Contains(screen) && screen.Visible;