feat(v3.2): 3MF format import/export

include/vde/foundation/io_3mf.h

@@ -0,0 +1,27 @@
+#pragma once
+#include "vde/mesh/halfedge_mesh.h"
+#include <string>
+#include <vector>
+
+namespace vde::foundation {
+
+/// 3MF mesh data with optional vertex colors
+struct ThreeMFMesh {
+    mesh::HalfedgeMesh mesh;
+    std::string name;
+    std::vector<float> vertex_colors;  ///< optional RGB per vertex (3*nv floats)
+};
+
+/// Read a 3MF file and return all meshes
+[[nodiscard]] std::vector<ThreeMFMesh> read_3mf(const std::string& filepath);
+
+/// Write meshes to a 3MF file
+/// @param filepath Output .3mf file
+/// @param meshes Mesh list to export
+/// @param creator Application name (stored in metadata)
+/// @return true on success
+bool write_3mf(const std::string& filepath,
+               const std::vector<ThreeMFMesh>& meshes,
+               const std::string& creator = "ViewDesignEngine");
+
+}  // namespace vde::foundation