Phase 6 commit A：AppCoordinator + SubGameViewController 框架 + SwitchOverGameData push

- AppCoordinator：2s 节流 + 栈深 < 2 守门 + .subGameDidReturn 通知名（Design §2.4.3）
- SubGameViewController：复用 BridgedWebView/Splash/16:9 letterbox/ExternalSubscriptions，
  AppDataWriter(.subGame) 写 4 个 app_*.js；H5 未安装时抛错（待 commit B 接入下载）
- SwitchOverGameHandler：解 Gamedirectory/gamedownloadurl/data → AppCoordinator.showSubGame
  （msext NewRootVC.m:541-566 等价，节流与栈深由 Coordinator 守门，cb 字面始终回）
- SceneDelegate：UINavigationController 承载大厅，nav 引用交给 AppCoordinator
- Plan 进度已勾选 §5 / §8（commit B/C 留待 SubGameDownloader 与 backgameData/getWebdata 链路）

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ylgamehall/SceneDelegate.swift

@@ -14,7 +14,17 @@ final class SceneDelegate: UIResponder, UIWindowSceneDelegate {
                options connectionOptions: UIScene.ConnectionOptions) {
         guard let windowScene = scene as? UIWindowScene else { return }
         let window = UIWindow(windowScene: windowScene)
-        window.rootViewController = WebContainerViewController()
+
+        // 用 UINavigationController 承载大厅，便于 Phase 6 push 子游戏 / Phase 7 push 弹层。
+        // 栈深约束 ≤ 3（Design §2.4.3），由 AppCoordinator 在 push 处守门。
+        let lobby = WebContainerViewController()
+        let nav = UINavigationController(rootViewController: lobby)
+        nav.setNavigationBarHidden(true, animated: false)
+        nav.interactivePopGestureRecognizer?.isEnabled = false
+
+        AppCoordinator.shared.navigationController = nav
+
+        window.rootViewController = nav
         self.window = window
         window.makeKeyAndVisible()
     }