Environment settings become scene entities (UE Skybox/SkyLight semantics)

Skybox/SkyLight are now Actor-carried components instead of resident
global settings, matching UE where SkyAtmosphere/SkyLight/fog are
Actors added from Place Actors and configured in Details.

- New SkyboxComponent (active + envPath asset slot) and SkyLightComponent
  (active + ambientColor); first-active entity wins per frame
- SceneRenderer collects env from components into FrameSceneData
  (DrawSkybox/envPath/ambient); Renderer performs delta sync - env
  reloads only when the resolved path changes, neutral fallback when
  empty or unloadable
- App-side env plumbing removed: kEnvPaths table and getEnvIndex/
  setEnvIndex callbacks deleted; StatsPanel keeps ClearColor + debug
  view, env params move to Details
- Serializer: scene-level Settings stores ClearColor only; env
  components serialize per entity; legacy v1 scenes (Environment header
  + Settings.AmbientColor/DrawSkybox) auto-migrate into an Environment
  entity on load for visual parity
- Inspector: Skybox/Sky Light sections with .hdr asset slot dropdown
  and Add Component entries; Outliner "+ Create" popup offers
  Empty/Light/Camera/Environment

App/editor/StatsPanel.cpp

@@ -120,34 +120,20 @@ void StatsPanel::Draw(const EditorContext& ctx)
         }
     }
 
-    // ---- Environment：IBL 环境 + 调试视图（决定"看什么"）----
+    // ---- Environment：清屏色 + 调试视图（决定"看什么"）。
+    //      环境贴图/环境光已迁为实体组件（Skybox/SkyLight），在 Details 配 ----
     if (ImGui::CollapsingHeader("Environment", ImGuiTreeNodeFlags_DefaultOpen))
     {
-        bool& drawSkybox = ctx.scene->GetSettings().DrawSkybox;
-        ImGui::Checkbox("DrawSkybox", &drawSkybox);
-        if (drawSkybox && ctx.getEnvIndex)
-        {
-            int envIdx = ctx.getEnvIndex();
-            if (ImGui::Combo("env", &envIdx, kEnvNames, kEnvCount))
-            {
-                ctx.setEnvIndex(envIdx);
-                const auto env = ctx.assets->LoadEnvironment(kEnvPaths[envIdx]);
-                ctx.renderer->SetEnvironment(ctx.assets->GetEnvironment(env));
-            }
+        ImGui::ColorEdit4("ClearColor",
+                          glm::value_ptr(ctx.scene->GetSettings().ClearColor));
 
-            // 调试视图：单看某个 pass 的中间输出（类 UE pass debug）
-            const auto& viewNames = renderer.GetDebugViewNames();
-            int view = renderer.GetDebugView();
-            if (ImGui::Combo("Debug View", &view, viewNames.data(),
-                             static_cast<int>(viewNames.size())))
-            {
-                renderer.SetDebugView(view);
-            }
-        }
-        else
+        // 调试视图：单看某个 pass 的中间输出（类 UE pass debug）
+        const auto& viewNames = renderer.GetDebugViewNames();
+        int view = renderer.GetDebugView();
+        if (ImGui::Combo("Debug View", &view, viewNames.data(),
+                         static_cast<int>(viewNames.size())))
         {
-            ImGui::ColorEdit4("ClearColor",
-                              glm::value_ptr(ctx.scene->GetSettings().ClearColor));
+            renderer.SetDebugView(view);
         }
     }