feat: LOD 运行时开关（ImGui Features 横排，关 = 实例收集恒选 LOD0）

Engine/src/Renderer/SceneRenderer.cpp

@@ -174,6 +174,7 @@ namespace Engine
         m_Frame.shadowsEnabled = m_ShadowsEnabled;
         m_Frame.taaEnabled = m_TAAEnabled;
         m_Frame.bloomEnabled = m_BloomEnabled;
+        m_Frame.lodEnabled = m_LodEnabled;
         m_Frame.debugView = m_DebugView;
         ubo.cascadeSplits.w = m_ShadowsEnabled ? 1.0f : 0.0f;
 
@@ -315,14 +316,16 @@ namespace Engine
                     const f32 worldRadius = bounds.radius * worldScale;
 
                     // LOD 选级：屏占比近似 = radius/距离（主视图按实例距离；
-                    // 阈值 10/20 倍半径，可调）
+                    // 阈值 10/20 倍半径，可调）。开关关闭 = 恒 LOD0
                     const f32 dist =
                         glm::length(worldCenter - camTransform->GetPosition());
                     u32 mainLod = 0;
-                    if (dist >= worldRadius * 20.0f) {
-                        mainLod = 2;
-                    } else if (dist >= worldRadius * 10.0f) {
-                        mainLod = 1;
+                    if (m_LodEnabled) {
+                        if (dist >= worldRadius * 20.0f) {
+                            mainLod = 2;
+                        } else if (dist >= worldRadius * 10.0f) {
+                            mainLod = 1;
+                        }
                     }
 
                     auto tryAppend = [&](ViewScratch& s, const Frustum& frustum,
@@ -361,9 +364,9 @@ namespace Engine
                     for (u32 c = 0; c < kMaxCascades; ++c) {
                         if (!cascVis[c]) continue;   // 粗剔除已判不可见
                         // 级联降级：越远的级联覆盖范围越大，用越低的 LOD
-                        //（阴影本来就是低频信息，误差可接受）
+                        //（阴影本来就是低频信息，误差可接受）；开关关闭 = 恒 LOD0
                         tryAppend(m_CascScratch[c], cascFrustum[c],
-                                  std::min(c, kMeshLodCount - 1));
+                                  m_LodEnabled ? std::min(c, kMeshLodCount - 1) : 0u);
                     }
                 }
             });