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/EditorContext.h

@@ -15,22 +15,6 @@
 #include <Engine/Renderer/EditorCamera.h>
 #include <Engine/Renderer/SceneTypes.h>   // kDisplayViewport / kDisplayDirect
 
-#include <functional>
-
-// 可切换环境（IBL 动态切换）：StatsPanel 的 Combo 与 SandboxApp 的
-// 加载逻辑共用这一张表（下标即身份）。
-inline constexpr const char *kEnvPaths[] = {
-    "assets/textures/venice_dawn_1_4k.hdr",
-    "assets/textures/rooitou_park_4k.hdr",
-    "assets/textures/pink_sunrise_4k.hdr",
-    "assets/textures/birchwood_4k.hdr",
-};
-inline constexpr const char *kEnvNames[] = {
-    "Venice Dawn", "Rooitou Park", "Pink Sunrise", "Birchwood",
-};
-inline constexpr int kEnvCount = 4;
-inline constexpr int kDefaultEnv = 0;
-
 // 沙盒特有状态（面板可选读取，空指针 = 该面板区块不显示）
 struct EditorContext {
     // 引擎门面
@@ -45,9 +29,6 @@ struct EditorContext {
     // PIE 运行态（Play-In-Editor）：Editor 持有，只读指针。
     // 面板门控用——运行态禁 Gizmo/编辑器热键，渲染源已是 primary 相机
     const bool *playState = nullptr;
-
-    std::function<int()> getEnvIndex; // 当前环境表下标
-    std::function<void(int)> setEnvIndex;
 };
 
 #endif //HELLOVULKAN_EDITORCONTEXT_H