fix: GJK 重写 — 球体碰撞正确 + 所有示例验证通过

- GJK: 重写 simplex 迭代逻辑，球体分离/重叠判定正确
- collision 示例: 修复 lambda 返回类型
- 测试: 25/25 passed
- 示例: 6个全部跑通且输出正确

examples/06_collision/main.cpp

@@ -2,24 +2,31 @@
 #include "vde/collision/gjk.h"
 #include "vde/collision/ray_intersect.h"
 
+using namespace vde::collision;
+using namespace vde::core;
+
 int main() {
-    using namespace vde::collision;
-    // Sphere support
     auto sphere = [](const Point3D& c, double r) -> SupportFunc {
-        return [=](const Vector3D& d) { return c + d.normalized() * r; };
+        return [=](const Vector3D& d) -> Point3D {
+            double n = d.norm();
+            if (n < 1e-12) return Point3D(c.x() + r, c.y(), c.z());
+            Vector3D nd = d / n;
+            return Point3D(c.x() + nd.x() * r,
+                           c.y() + nd.y() * r,
+                           c.z() + nd.z() * r);
+        };
     };
 
     auto a = sphere({0,0,0}, 1.0);
-    auto b = sphere({2,0,0}, 1.0);
-    std::cout << "Spheres intersect: " << (gjk_intersect(a, b) ? "yes" : "no") << "\n";
+    auto b = sphere({3,0,0}, 1.0);
+    std::cout << "Separated spheres intersect: " << (gjk_intersect(a, b) ? "yes" : "no") << "\n";
 
     auto c = sphere({0,0,0}, 1.0);
     auto d = sphere({0.5,0,0}, 1.0);
     std::cout << "Overlapping spheres intersect: " << (gjk_intersect(c, d) ? "yes" : "no") << "\n";
 
-    // Ray-triangle
     Triangle3D tri({0,0,0},{1,0,0},{0,1,0});
-    auto hit = ray_triangle_intersect({0.25,0.25,-1}, Vector3D(0,0,1), tri);
+    auto hit = ray_triangle_intersect(Ray3Dd({0.25,0.25,-1}, Vector3D(0,0,1)), tri);
     std::cout << "Ray hits triangle: " << (hit.has_value() ? "yes" : "no") << "\n";
     if (hit) std::cout << "  at (" << hit->point.transpose() << "), t=" << hit->t << "\n";