fix: Delaunay3D circumcenter 完整实现 + 测试恢复

tests/mesh/test_delaunay_3d.cpp

@@ -78,8 +78,6 @@ TEST(Delaunay3DTest, EmptyInput_ReturnsEmpty) {
 }
 
 TEST(Delaunay3DTest, FourPointsTetrahedron_OneTetrahedron) {
-    // NOTE: 3D Delaunay implementation is WIP — circumcenter formula incomplete.
-    // Once the Bowyer-Watson insertion is fixed, expect ≥1 tetrahedron.
     std::vector<Point3D> pts = {
         {1, 1, 1},
         {1, -1, -1},
@@ -88,12 +86,10 @@ TEST(Delaunay3DTest, FourPointsTetrahedron_OneTetrahedron) {
     };
     auto result = delaunay_3d(pts);
     EXPECT_EQ(result.vertices.size(), 4u);
-    // EXPECT_GE(result.tetrahedra.size(), 1u);  // TODO: fix circumcenter
+    EXPECT_GE(result.tetrahedra.size(), 1u);
 }
 
 TEST(Delaunay3DTest, FivePointsCube_VerifyDelaunayProperty) {
-    // 4 corners of a tetrahedron + 1 point inside the circumsphere
-    // Use a well-distributed set: origin + unit tetrahedron
     std::vector<Point3D> pts = {
         {0, 0, 0},
         {1, 0, 0},
@@ -103,11 +99,10 @@ TEST(Delaunay3DTest, FivePointsCube_VerifyDelaunayProperty) {
     };
     auto result = delaunay_3d(pts);
     EXPECT_EQ(result.vertices.size(), 5u);
-    // EXPECT_GE(result.tetrahedra.size(), 2u);  // TODO: fix circumcenter
+    EXPECT_GE(result.tetrahedra.size(), 2u);
 }
 
 TEST(Delaunay3DTest, FivePointsDelaunayProperty_EmptyCircumsphere) {
-    // Regular tetrahedron + center point — should satisfy Delaunay
     std::vector<Point3D> pts = {
         {1, 1, 1},
         {1, -1, -1},
@@ -117,8 +112,8 @@ TEST(Delaunay3DTest, FivePointsDelaunayProperty_EmptyCircumsphere) {
     };
     auto result = delaunay_3d(pts);
     EXPECT_EQ(result.vertices.size(), 5u);
-    // EXPECT_GE(result.tetrahedra.size(), 4u);  // TODO: fix circumcenter
-    (void)result;
+    EXPECT_GE(result.tetrahedra.size(), 4u);
+    EXPECT_TRUE(verify_empty_circumsphere(result, pts));
 }
 
 TEST(Delaunay3DTest, CollinearPoints_HandlesGracefully) {