PIE: viewport-embedded playback with UE-style main toolbar

Play no longer switches to fullscreen direct rendering: PIE now keeps
the editor UI alive and renders the primary camera into the Viewport
panel (new SceneRenderer::SetGameView flag; kDisplayDirect stays a
manual fullscreen preview for later release form). Editor camera stops
being driven during PIE, and viewport click-pick is gated off while
playing (clicks are game input now).

The Play/Stop buttons move out of the menu bar into a dedicated main
toolbar row below it (centered, UE Main Toolbar semantics): green Play
when idle; Pause (yellow, highlighted while paused) + Stop (orange)
while playing. Ctrl+P hotkey kept. Stats "Pause Simulation" merged
into the toolbar Pause; viewport overlay shows PAUSED accordingly.

App/editor/Editor.h

@@ -57,12 +57,16 @@ public:
     // 请求退出（弹确认框；窗口关闭事件走这里）
     void RequestQuit() { m_ShowQuitConfirm = true; }
 
-    // ---- PIE（Play-In-Editor，UE 工具栏语义）----
+    // ---- PIE（Play-In-Editor，UE 主工具栏语义）----
     bool IsPlaying() const { return m_Playing; }
-    // Play：内存快照当前场景 → 切游戏渲染（primary 相机）→ 解冻时间；
+    bool IsPaused() const { return m_Paused; }
+    // Play：内存快照当前场景 → 切 gameView（Viewport 内嵌 primary 相机
+    // 渲染，UE PIE 语义；不切全屏）→ 解冻时间；
     // Stop：快照原子换血恢复 → 回编辑器渲染 → 冻结时间。
     // 编辑器态默认 timeScale=0（物理冻结 = UE 语义），Play 解冻
     void TogglePlay();
+    // PIE 暂停切换（UE Pause 语义）：timeScale 0 ↔ 1
+    void TogglePause();
 
 private:
     void DoPlay();    // TogglePlay 的 Play 半程（快照 + 切渲染 + 解冻）
@@ -86,7 +90,8 @@ private:
     entt::entity GetSelected() const { return m_Selected; }
 
 private:
-    void DrawMenuBar();       // host 窗口内顶栏
+    void DrawMenuBar();       // host 窗口内顶栏（File/View 菜单）
+    void DrawToolbar();       // 菜单栏下方主工具栏（Play/Pause/Stop 居中）
     void DrawDockSpace();     // 全屏 host + dockspace + 默认布局
     void DrawQuitModal();     // 退出确认模态框
     void DrawSceneModals();   // 保存/加载路径模态框（共用一个路径输入）
@@ -127,6 +132,7 @@ private:
 
     // PIE 状态：Play 时场景 YAML 内存快照，Stop 时原子换血恢复
     bool m_Playing = false;
+    bool m_Paused = false;   // PIE 暂停（timeScale=0；Stop 时复位）
     std::string m_PlaySnapshot;
 };