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

src/foundation/exact_predicates.cpp

@@ -63,6 +63,8 @@ struct Expansion {
     }
 };
 
+} // namespace (anonymous)
+
 // ── orient_2d with expansion arithmetic ──
 Orientation orient_2d(const Point2D& a, const Point2D& b, const Point2D& c) {
     double acx = a.x() - c.x(), acy = a.y() - c.y();
@@ -193,5 +195,4 @@ CircleTest in_circle(const Point2D& a, const Point2D& b,
     return CircleTest::On;
 }
 
-}  // namespace
 }  // namespace vde::foundation::exact