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.

Engine/src/Renderer/SceneRenderer.cpp

@@ -269,12 +269,13 @@ namespace Engine
         ubo.prevView = m_LastView;
         ubo.prevProj = m_LastProjNoJitter;
 
-        // ---- 1. 相机：渲染源按显示模式分派（UE 语义）。编辑器形态
+        // ---- 1. 相机：渲染源按形态分派（UE 语义）。编辑器形态
         //         Scene view 恒用编辑器相机（视口 UI 状态，空场景可用）；
-        //         游戏形态用场景 primary 相机实体（游戏逻辑所有）----
+        //         游戏形态（kDisplayDirect 全屏预览或 PIE 内嵌播放）用
+        //         场景 primary 相机实体（游戏逻辑所有）----
         ECS::TransformComponent* camTransform = nullptr;
         const Camera* camera = nullptr;
-        if (m_DisplayMode == kDisplayViewport) {
+        if (m_DisplayMode == kDisplayViewport && !m_GameView) {
             camTransform = &m_EditorCamera.GetTransform();
             camera = &m_EditorCamera.GetController();
         } else if (auto* cameraComp = scene.GetPrimaryCamera(&camTransform)) {