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/StatsPanel.cpp

@@ -25,6 +25,9 @@ void StatsPanel::Draw(const EditorContext& ctx)
     // ---- View：看哪里（渲染目标）+ 相机位姿（跟随渲染源分派）----
     if (ImGui::CollapsingHeader("View", ImGuiTreeNodeFlags_DefaultOpen))
     {
+        // 渲染源分派与 SceneRenderer::BuildFrame 同规则：PIE 内嵌播放
+        // 或 kDisplayDirect 全屏预览 = primary 相机，否则编辑器相机
+        const bool playing = ctx.playState && *ctx.playState;
         static const char* displayTarget[] = {
             "Fullscreen",
             "Viewport",
@@ -35,13 +38,7 @@ void StatsPanel::Draw(const EditorContext& ctx)
         {
             renderer.SetDisplayMode(mode);
         }
-        if (renderer.GetDisplayMode() == kDisplayViewport && ctx.editorCamera)
-        {
-            const glm::vec3& pos = ctx.editorCamera->GetTransform().GetPosition();
-            ImGui::Text("Editor Camera Pos");
-            ImGui::Text("(%.3f, %.3f, %.3f)", pos.x, pos.y, pos.z);
-        }
-        else
+        if ((playing || renderer.GetDisplayMode() == kDisplayDirect))
         {
             Engine::ECS::TransformComponent* camT = nullptr;
             if (ctx.scene->GetPrimaryCamera(&camT) != nullptr && camT != nullptr)
@@ -56,17 +53,21 @@ void StatsPanel::Draw(const EditorContext& ctx)
                 ImGui::TextDisabled("(no primary camera)");
             }
         }
+        else if (ctx.editorCamera)
+        {
+            const glm::vec3& pos = ctx.editorCamera->GetTransform().GetPosition();
+            ImGui::Text("Editor Camera Pos");
+            ImGui::Text("(%.3f, %.3f, %.3f)", pos.x, pos.y, pos.z);
+        }
+        else
+        {
+            ImGui::TextDisabled("(no camera)");
+        }
     }
 
-    // ---- Scene：模拟控制 + 场景级设置 ----
+    // ---- Scene：模拟控制 + 场景级设置。PIE 暂停在主工具栏（UE 语义）----
     if (ImGui::CollapsingHeader("Scene", ImGuiTreeNodeFlags_DefaultOpen))
     {
-        // 暂停模拟（引擎 Time 门面：动画/物理统一冻结）
-        bool paused = Time::TimeScale() == 0.0f;
-        if (ImGui::Checkbox("Pause Simulation", &paused))
-        {
-            Time::SetTimeScale(paused ? 0.0f : 1.0f);
-        }
         ImGui::ColorEdit4("Clear Color",
                           glm::value_ptr(ctx.scene->GetSettings().ClearColor));
     }