Improve PBR quality: mip chains, anisotropic filtering, baseColorFactor

Root causes behind blurry/unphysical materials (4K pocket watch render
mushy, glass fully opaque, watch hands unreadable):

- Textures loaded via stbi had a single mip level: 4096x4096 albedo/MR
  maps sampled with no LOD -> minification aliasing turned fine detail
  (watch hands) into noise. Generate a full blit-based mip chain with
  per-level layout transitions.
- samplerAnisotropy was never enabled on the device and every sampler
  was created with anisotropy disabled: grazing-angle surfaces (watch
  face, ground) collapsed into a blur. Enable the device feature and
  16x anisotropic filtering on material texture samplers.
- glTF baseColorFactor was ignored: the glass material (alphaMode
  BLEND, no baseColor texture, baseColorFactor.a = 0.3) fell back to
  the default white texture with alpha = 1 and rendered fully opaque.
  MaterialParams gains a baseColor vec4 (rgb tints albedo, a scales
  the blend alpha) threaded through both PBR shaders.
- alphaMode MASK was treated as opaque: add a factors.w switch that
  performs an alpha cutout test in the opaque shader.
- Fix material cache key dropping factors.z (separate-roughness
  switch); it now encodes the full factors and baseColor vectors.

Engine/src/Renderer/Model.cpp

@@ -695,12 +695,27 @@ ParsedMesh Model::ProcessMesh(const aiMesh* mesh, const aiScene* scene,
             params.factors = glm::vec4(static_cast<f32>(metallic),
                                        static_cast<f32>(roughness), 0.0f, 0.0f);
 
-            // glTF alphaMode：BLEND = 半透明（透明绘制队列 + 深度只测不写）。
-            // MASK（alpha cutout）暂按不透明——需要 alpha test，后续演进。
+            // baseColorFactor：rgb 调色进 albedo；a 是 BLEND 材质的透明度
+            //（玻璃等无 baseColor 贴图、纯靠 factor alpha 的材质全靠它，
+            // 缺了会退化成兜底白纹理的 a=1 = 完全不透）
+            aiColor4D baseColor(1.0f, 1.0f, 1.0f, 1.0f);
+            if (material->Get(AI_MATKEY_BASE_COLOR, baseColor) == AI_SUCCESS) {
+                params.baseColor = glm::vec4(baseColor.r, baseColor.g,
+                                             baseColor.b, baseColor.a);
+            }
+
+            // glTF alphaMode：
+            //   BLEND = 半透明（透明绘制队列 + 深度只测不写）
+            //   MASK  = 镂空（factors.w=1 → shader 侧 alpha test 丢弃，
+            //           表针/栅栏等硬边贴图常见）仍走不透明队列
             // OBJ/FBX 无此键 → 恒不透明（资产格式定义写死）
             aiString alphaMode;
             if (material->Get(AI_MATKEY_GLTF_ALPHAMODE, alphaMode) == AI_SUCCESS) {
-                out.transparent = (alphaMode == aiString("BLEND"));
+                if (alphaMode == aiString("BLEND")) {
+                    out.transparent = true;
+                } else if (alphaMode == aiString("MASK")) {
+                    params.factors.w = 1.0f;
+                }
             }
         } else {
             // FBX/OBJ 独立贴图工作流