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.

shaders/simple_shader.frag

@@ -42,7 +42,8 @@ layout(set = 1, binding = 3) uniform sampler2D emissiveMap;
 layout(set = 1, binding = 4) uniform sampler2D aoMap;   // 环境光遮蔽（R 通道）
 layout(set = 1, binding = 5) uniform sampler2D roughnessMap;  // 独立粗糙度图（R 通道，specular 工作流）
 layout(set = 1, binding = 6) uniform MaterialParams {
-    vec4 factors;   // x = metallic 因子，y = roughness 因子，z = 独立粗糙度图开关
+    vec4 factors;     // x = metallic 因子，y = roughness 因子，z = 独立粗糙度图开关，w = MASK 镂空开关
+    vec4 baseColor;   // glTF baseColorFactor：rgb 调色 albedo，a = BLEND 透明度
 } matParams;
 
 // CSM 阴影（sampler2DShadow：单次采样 = 硬件 2×2 深度比较 PCF）
@@ -136,7 +137,9 @@ vec3 FresnelSchlickRoughness(float cosTheta, vec3 F0, float roughness) {
 
 void main() {
     vec4 albedoTex = texture(albedoMap, fragUV);
-    vec3 albedo = albedoTex.rgb;
+    // alphaMode=MASK 镂空（表针/栅栏等硬边贴图）：低于阈值的纹素直接丢弃
+    if (matParams.factors.w > 0.5 && albedoTex.a < 0.5) discard;
+    vec3 albedo = albedoTex.rgb * matParams.baseColor.rgb;
     vec4 mr = texture(metallicRoughnessMap, fragUV);
     // 粗糙度源按 factors.z 切换：glTF 合图工作流读 MR.g；
     // FBX/OBJ specular 工作流（z=1）换用独立粗糙度图 R 通道
@@ -223,8 +226,8 @@ void main() {
     vec3 ambient = (diffuse + specular) * ubo.ambientColor.rgb
                    * mix(0.4, 1.0, shade0);   // 阴影区环境同步衰减（简化遮蔽）
 
-    // alpha = albedo 贴图覆盖率（glTF alphaMode=BLEND 混合源）；
-    // 不透明资产贴图 a=1 行为不变。预乘在 tonemap 段完成。
-    outColor = vec4(ambient + Lo + emissive, albedoTex.a);
+    // alpha = albedo 贴图覆盖率 × baseColorFactor.a（glTF alphaMode=BLEND
+    // 混合源）；不透明资产两者恒 1 行为不变。预乘在 tonemap 段完成。
+    outColor = vec4(ambient + Lo + emissive, albedoTex.a * matParams.baseColor.a);
     outVelocity = fragVelocity;
 }