fix: ReadOnlyPropertyDrawer + BoardManager skips PlacePieces in campaign mode

I1: ReadOnlyDrawer shows [ReadOnly] fields as greyed out in Inspector
I2: BoardManager.Start() skips PlacePieces() when CampaignManager is active (SetupBoard will place pieces instead)

Assets/Editor/ReadOnlyDrawer.cs

@@ -0,0 +1,16 @@
+using UnityEditor;
+using UnityEngine;
+
+/// <summary>
+/// PropertyDrawer for ReadOnlyAttribute. Shows fields as disabled (greyed out) in the Inspector.
+/// </summary>
+[CustomPropertyDrawer(typeof(ReadOnlyAttribute))]
+public class ReadOnlyDrawer : PropertyDrawer
+{
+    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
+    {
+        GUI.enabled = false;
+        EditorGUI.PropertyField(position, property, label);
+        GUI.enabled = true;
+    }
+}

Assets/Game/Scripts/Mono/BoardManager.cs

@@ -57,8 +57,11 @@ public GameObject kingPrefab; // Prefab del Rey usado como "jefe" en el purgator
         GenerateBoard();
         GenerateIndicators();
         
-        // Setup estándar (puede ser reemplazado por SetupBoard con CampaignState)
-        PlacePieces();
+        // Skip standard piece placement if CampaignManager will call SetupBoard
+        if (CampaignManager.Instance == null || !CampaignManager.Instance.IsCampaignActive)
+        {
+            PlacePieces();
+        }
     }
     
     /// <summary>