feat: 解析式 PBR（Cook-Torrance GGX，metallic-roughness 工作流）

- 修 void* 指针算术警告（Texture::InitFromDds）
- Material：slot2 语义切为 metallicRoughness（glTF 约定 G=粗糙度
  B=金属度）+ 新增材质因子参数 UBO（binding 4，per-slot ring，
  创建时写死，metallic/roughness 因子乘 MR 贴图）
- simple_shader.frag：Blinn-Phong → Cook-Torrance（GGX 分布 +
  Smith 几何 + Schlick Fresnel，k=(r+1)²/8 解析光源版）；金属不参与
  漫反射；环境光暂为常数（IBL 后续）
- Model：读 aiTextureType_UNKNOWN（glTF MR 落点）+ AI_MATKEY_
  METALLIC/ROUGHNESS_FACTOR（旧资产缺键退化为电介质 0/0.5）；
  材质缓存键含因子
- main.cpp：演示场景换回 backpack（旧资产走因子路径验证 PBR 全链路）
- 旧 specular 贴图不再使用（语义被 MR 取代）

Engine/src/Renderer/Material.cpp

@@ -7,14 +7,17 @@
 #include <Engine/Vulkan/MemoryAllocator.h>
 #include <Engine/Vulkan/DescriptorManager.h>
 #include <Engine/Vulkan/Texture.h>
+#include <Engine/Vulkan/UniformBuffer.h>
+#include <Engine/Core/FrameContext.h>
 #include <Engine/Core/Log.h>
 
 namespace Engine
 {
-    Material::Material(Device& device,
+    Material::Material(Device& device, MemoryAllocator& allocator,
                        DescriptorManager& descriptorManager,
                        vk::DescriptorSetLayout layout,
-                       const std::array<Texture*, kSlotCount>& textures)
+                       const std::array<Texture*, kSlotCount>& textures,
+                       const MaterialParams& params)
     : m_Textures(textures)
     {
         m_DescriptorSet = descriptorManager.AllocateDescriptorSet(layout);
@@ -25,18 +28,31 @@ namespace Engine
                 m_Textures[slot]->GetSampler(),
                 m_Textures[slot]->GetView());
         }
+
+        // 材质参数：per-slot ring，创建时写死（参数静态，无每帧更新）
+        m_ParamsBuffer = CreateScope<UniformBuffer>(
+            device, allocator, sizeof(MaterialParams), kMaxFramesInFlight);
+        for (u32 slot = 0; slot < kMaxFramesInFlight; ++slot) {
+            m_ParamsBuffer->Update(slot, &params, sizeof(params));
+            descriptorManager.UpdateUniformBuffer(
+                m_DescriptorSet, kParamsBinding,
+                m_ParamsBuffer->Get(slot), m_ParamsBuffer->GetSize());
+        }
     }
 
 
     Material::~Material() = default;
 
-    std::string Material::MakeCacheKey(const std::string paths[kSlotCount])
+    std::string Material::MakeCacheKey(const std::string paths[kSlotCount],
+                                       const MaterialParams& params)
     {
         std::string key;
         for (u32 slot = 0; slot < kSlotCount; ++slot) {
-            if (slot) key += '\n';
             key += paths[slot];
+            key += '\n';
         }
+        key += "f:" + std::to_string(params.factors.x) +
+               "," + std::to_string(params.factors.y);
         return key;
     }
 } // namespace Engine