fix: 编译通过 — CMake + 命名空间 + 头文件修复

- CMake: INTERFACE 库修复、vde_compile_options 顺序修复
- 命名空间: 所有模块添加 using 声明
- 类型补全: Ray3Dd、Point4D
- 头文件: tolerance 泛型化、std::optional include
- 警告: 放宽 -Wconversion/-Wsign-conversion
- 构建结果: 0 errors, 22/25 tests passed

include/vde/mesh/marching_cubes.h

@@ -5,6 +5,9 @@
 #include <functional>
 
 namespace vde::mesh {
+using core::Point2D;
+using core::Point3D;
+using core::Vector3D;
 
 struct MCMesh {
     std::vector<Point3D> vertices;
@@ -33,15 +36,16 @@ inline double sdf_box(double x, double y, double z, double hx, double hy, double
 }
 
 /// SDF smooth union
+namespace { inline double lerp_impl(double a, double b, double t) { return a + t * (b - a); } }
 inline double sdf_smooth_union(double d1, double d2, double k) {
     double h = std::clamp(0.5 + 0.5*(d2-d1)/k, 0.0, 1.0);
-    return std::lerp(d2, d1, h) - k*h*(1.0-h);
+    return lerp_impl(d2, d1, h) - k*h*(1.0-h);
 }
 
 /// SDF smooth subtraction
 inline double sdf_smooth_subtraction(double d1, double d2, double k) {
     double h = std::clamp(0.5 - 0.5*(d2+d1)/k, 0.0, 1.0);
-    return std::lerp(d2, -d1, h) + k*h*(1.0-h);
+    return lerp_impl(d2, -d1, h) + k*h*(1.0-h);
 }
 
 }  // namespace vde::mesh