feat: P2 Alpha Shapes + 网格参数化

- mesh: Alpha Shapes (点云→表面)
- mesh: Tutte 嵌入参数化
- mesh: LSCM 保角参数化
- 新增 4 文件，更新 CMake

include/vde/mesh/alpha_shapes.h

@@ -0,0 +1,17 @@
+#pragma once
+#include "vde/core/point.h"
+#include "vde/mesh/delaunay_3d.h"
+#include <vector>
+
+namespace vde::mesh {
+
+/// Alpha Shapes: extract surface from point cloud
+/// For alpha → ∞, returns convex hull; for alpha → 0, returns all faces
+/// @param alpha  Radius threshold: faces with circumradius > alpha are removed
+TetrahedronMesh alpha_shapes(const std::vector<Point3D>& points, double alpha);
+
+/// Convert alpha shapes tet mesh to triangle surface
+std::pair<std::vector<Point3D>, std::vector<std::array<int,3>>>
+alpha_shapes_surface(const TetrahedronMesh& tet_mesh);
+
+}  // namespace vde::mesh