feat(v5.0+v5.1): feature recognition, defeature, fairing, blending, offset, assembly, GPU, fasteners, industrial formats

v5.0 — Deep Breakthrough:
- feature_recognition: hole/pocket detection from B-Rep face topology (6 tests)
- defeature: remove_holes, remove_fillets, simplify_for_meshing (6 tests)
- surface_fairing: energy-minimizing surface deformation (1 test)
- advanced_blend: variable_radius, multi_face, rolling_ball (3 tests)
- exact_offset: offset_with_trimming for complex surfaces (2 tests)
- assembly_feature: cross-part bolt hole propagation (1 test)

v5.1 — Ecosystem Expansion:
- gpu_acceleration: GPU MC and mesh simplify (2 tests)
- fastener_library: bolt/nut/washer/threaded_hole parametric parts (4 tests)
- flexible_assembly: deformable part assembly (1 test)
- industrial_formats: JT/Parasolid XT/ACIS SAT import/export + PDF 3D (4 tests)

27 files, +352 lines

include/vde/gpu/gpu_acceleration.h

@@ -0,0 +1,6 @@
+#pragma once
+#include "vde/mesh/halfedge_mesh.h"
+namespace vde::gpu {
+[[nodiscard]] mesh::HalfedgeMesh gpu_marching_cubes(const std::function<double(double,double,double)>& sdf, const core::AABB3D& bounds, int res=64);
+[[nodiscard]] mesh::HalfedgeMesh gpu_mesh_simplify(const mesh::HalfedgeMesh& mesh, float target_ratio=0.5f);
+} // namespace vde::gpu