chore: add idempotent Main prefab connection entry

Assets/MagnetismHeroes/Editor/ProjectBootstrap.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Linq;
 using UnityEditor;
 using UnityEditor.Build.Reporting;
 using UnityEditor.SceneManagement;
@@ -46,6 +47,26 @@ namespace MagnetismHeroes.Editor
             Debug.Log("[Scaffold] Unity project prepared.");
         }
 
+        public static void ConnectApp()
+        {
+            const string prefabPath = "Assets/MagnetismHeroes/UnityRuntime/Presentation/Prefabs/GameApp.prefab";
+            var prefab = AssetDatabase.LoadAssetAtPath<GameObject>(prefabPath);
+            if (prefab == null) throw new InvalidOperationException("GameApp prefab missing.");
+            var scene = EditorSceneManager.OpenScene(MainScenePath, OpenSceneMode.Single);
+            var instances = scene.GetRootGameObjects().Where(root =>
+                PrefabUtility.GetPrefabAssetPathOfNearestInstanceRoot(root) == prefabPath).ToArray();
+            if (instances.Length > 1) throw new InvalidOperationException("Main contains duplicate GameApp instances.");
+            foreach (var root in scene.GetRootGameObjects())
+            {
+                if ((root.name == "Main Camera" && root.GetComponent<Camera>() != null)
+                    || (root.name == "Directional Light" && root.GetComponent<Light>() != null))
+                    UnityEngine.Object.DestroyImmediate(root);
+            }
+            if (instances.Length == 0) PrefabUtility.InstantiatePrefab(prefab, scene);
+            EditorSceneManager.SaveScene(scene, MainScenePath);
+            Debug.Log("[Integration] Main connected to GameApp.");
+        }
+
         public static void BuildAndroid()
         {
             string apkPath = Environment.GetEnvironmentVariable("MAGNETISM_APK_PATH");