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

Engine/src/Renderer/SceneRenderer.cpp

@@ -312,11 +312,35 @@ namespace Engine
             ubo.proj[2][1] += jy * 2.0f / static_cast<f32>(targetExtent.height);
         }
 
-        ubo.ambientColor = scene.GetSettings().AmbientColor;
+        // ---- 环境组件落帧（UE SkyLight/Skybox Actor 语义）：场景环境
+        //      是实体组件而非全局设置。多实例取第一个 active（entt
+        //      视图序 = 组件创建序，首个命中稳定）；无组件场景兜底 =
+        //      无天空 + 旧 Settings 默认环境光（空场景清屏可渲染）----
+        m_Frame.DrawSkybox = false;
+        m_Frame.envPath.clear();
+        ubo.ambientColor = glm::vec4{0.07f, 0.07f, 0.09f, 0.0f};
+        for (auto&& [e, sb] :
+             scene.GetRegistry().view<ECS::SkyboxComponent>().each())
+        {
+            if (sb.active)
+            {
+                m_Frame.DrawSkybox = true;
+                m_Frame.envPath = sb.envPath;
+                break;
+            }
+        }
+        for (auto&& [e, sl] :
+             scene.GetRegistry().view<ECS::SkyLightComponent>().each())
+        {
+            if (sl.active)
+            {
+                ubo.ambientColor = sl.ambientColor;
+                break;
+            }
+        }
 
         // ---- 运行时开关/调试视图落帧（各 pass 与 frag 只读契约字段）----
         m_Frame.ClearColor = scene.GetSettings().ClearColor;
-        m_Frame.DrawSkybox = scene.GetSettings().DrawSkybox;
         m_Frame.shadowsEnabled = m_ShadowsEnabled;
         m_Frame.taaEnabled = m_TAAEnabled;
         m_Frame.bloomEnabled = m_BloomEnabled;