Bind PaintHud to the scene-authored canvas

Drop the code-gen canvas/EventSystem bootstrap and the layoutPrefab
instantiation; the canvas and its panel now live in the scene, so PaintHud
binds to its first child at startup instead of building the UI at runtime.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scripts/Components/UI/PaintHud/PaintHud.cs

@@ -25,9 +25,6 @@ public partial class PaintHud : MonoBehaviour
     [Tooltip("Painter the HUD edits. Empty = the manager's painter, else found automatically.")]
     public MeshPainter painter;
 
-    [Tooltip("Authored panel layout. Instantiated and bound at startup.")]
-    public GameObject layoutPrefab;
-
     // Stable widget names shared by the baked prefab and the binder.
     private const string PanelGeneral = "Panel_General";
     private const string PanelSpray = "Panel_Spray";
@@ -111,16 +108,7 @@ public partial class PaintHud : MonoBehaviour
     private void Start()
     {
         _font = LoadFont();
-
-        EnsureEventSystem();
-        EnsureCanvas();
-
-        if (layoutPrefab)
-        {
-            var go = Instantiate(layoutPrefab, transform);
-            go.name = layoutPrefab.name; // strip the "(Clone)" suffix
-            _panel = go;
-        }
+        _panel = transform.GetChild(0).gameObject;
 
         // Snapshot the authored panel positions now, while the layout is untouched - before RestoreHudState
         // (in BindPainter) overwrites them. The reset button restores exactly these.
@@ -209,37 +197,6 @@ public partial class PaintHud : MonoBehaviour
         return f;
     }
 
-    // --- Canvas ---
-
-    private void EnsureCanvas()
-    {
-        var canvas = GetComponent<Canvas>();
-        if (!canvas) canvas = gameObject.AddComponent<Canvas>();
-        canvas.renderMode = RenderMode.ScreenSpaceOverlay;
-        canvas.sortingOrder = 100;
-
-        var scaler = GetComponent<CanvasScaler>();
-        if (!scaler) scaler = gameObject.AddComponent<CanvasScaler>();
-        scaler.uiScaleMode = CanvasScaler.ScaleMode.ScaleWithScreenSize;
-        scaler.referenceResolution = new Vector2(1920f, 1080f);
-        scaler.screenMatchMode = CanvasScaler.ScreenMatchMode.Expand;
-
-        if (!GetComponent<GraphicRaycaster>()) gameObject.AddComponent<GraphicRaycaster>();
-    }
-
-    private void EnsureEventSystem()
-    {
-        if (FindFirstObjectByType<EventSystem>()) return;
-
-        var es = new GameObject("EventSystem", typeof(EventSystem));
-#if ENABLE_INPUT_SYSTEM
-        var module = es.AddComponent<InputSystemUIInputModule>();
-        if (!module.actionsAsset) module.AssignDefaultActions();
-#else
-        es.AddComponent<StandaloneInputModule>();
-#endif
-    }
-
     // --- Wiring (behaviour; shared by the code-gen and prefab paths) ---
 
     private void WirePanel(Transform panel)