fix: 修复 7 个编译/测试问题 — 100% 测试通过

- exact_predicates: 匿名namespace泄漏导致orient_2d符号不可见
- mesh_quality: 纵横比公式归一化到[0,1], 1=等边三角形
- r_tree: insert/remove自赋值导致STR rebuild后数据丢失
- test_distance: PointToLine测试点在线上的错误断言
- test_smooth: 边界值断言从_LT改为_LE
- test_quality: 归一化纵横比的期望值调整

tests/core/test_distance.cpp

@@ -46,7 +46,7 @@ TEST(DistanceTest, PointToLine_OffsetOrigin) {
     Line3Dd line(Point3D(1,2,0), Vector3D(0,1,0));
     // Line through (1,2,0) along Y-axis
     // Point (1,0,0) → perpendicular distance = 2
-    EXPECT_DOUBLE_EQ(distance(Point3D(1,0,0), line), 2.0);
+    EXPECT_DOUBLE_EQ(distance(Point3D(3,0,0), line), 2.0);
 }
 
 // ── Point to Segment ──