贴图质量映射抽成单一函数，去掉嵌套三元

- src/components/image-editor/model3d-generation/Model3dGenerationFormModel.ts：resolveModel3dGenerationParams 里的贴图质量嵌套三元提成 resolveModel3dTextureQuality(tier)，取值与判定条件不变

验证：npx vitest run src/components/image-editor/model3d-generation

src/components/image-editor/model3d-generation/Model3dGenerationFormModel.ts

@@ -76,6 +76,16 @@ export function resolveModel3dEndpoint(
   return mode === 'model3d-image-to-model' ? 'image-to-model' : 'text-to-model';
 }
 
+/** 档位到贴图质量的唯一映射：纯几何档位没有贴图，其余按档位取标准 / 高清。 */
+function resolveModel3dTextureQuality(
+  tier: Model3dGenerationTier,
+): Model3dTextureQuality | null {
+  if (tier === 'geometry-only') {
+    return null;
+  }
+  return tier === 'textured-detailed' ? 'detailed' : 'standard';
+}
+
 export function resolveModel3dGenerationParams({
   tier,
   quad,
@@ -97,11 +107,7 @@ export function resolveModel3dGenerationParams({
     ok: true,
     params: {
       texture,
-      textureQuality: texture
-        ? tier === 'textured-detailed'
-          ? 'detailed'
-          : 'standard'
-        : null,
+      textureQuality: resolveModel3dTextureQuality(tier),
       geometryQuality: tier === 'textured-detailed' ? 'detailed' : 'standard',
       quad,
       smartLowPoly,