feat: v0.5.0 P1 + 差异化功能 — Voronoi, Marching Cubes, 曲率, 序列化, Python绑定

新增功能：
- core: 2D Voronoi 图（Delaunay 对偶图）
- mesh: Marching Cubes（完整256项三角表 + SDF 辅助函数）
- mesh: 离散曲率（Gaussian/Mean, Cotan 公式）
- foundation: 二进制序列化（版本化格式，Little-Endian）
- python: pybind11 绑定（30+ API 暴露）
- marching_cubes.h: SDF 基本体（球/盒）+ 光滑布尔

include/vde/foundation/serializer.h

@@ -0,0 +1,38 @@
+#pragma once
+#include "vde/mesh/halfedge_mesh.h"
+#include <vector>
+#include <cstdint>
+#include <string>
+
+namespace vde::foundation {
+
+// Versioned binary format for fast save/load
+// Header: 8 bytes magic + 4 bytes version + 4 bytes flags
+
+constexpr uint64_t VDE_MAGIC = 0x56444547454F4D00ULL; // "VDEGEOM\0"
+constexpr uint32_t VDE_FORMAT_VERSION = 1;
+
+struct SerializedMesh {
+    uint32_t vertex_count;
+    uint32_t face_count;
+    std::vector<double> vertices;     // xyz xyz ... (flat)
+    std::vector<int32_t> face_indices; // v0 v1 v2 ...
+    std::vector<int32_t> face_valence; // 3 for all triangles
+};
+
+class BinarySerializer {
+public:
+    /// Serialize mesh to binary buffer
+    static std::vector<uint8_t> serialize(const HalfedgeMesh& mesh);
+
+    /// Deserialize mesh from binary buffer
+    static HalfedgeMesh deserialize(const std::vector<uint8_t>& data);
+
+    /// Write to file
+    static bool write_file(const std::string& path, const HalfedgeMesh& mesh);
+
+    /// Read from file
+    static HalfedgeMesh read_file(const std::string& path);
+};
+
+}  // namespace vde::foundation