08b5854c56
Add batch evaluation/gradient functions for SDF trees (sdf_torch.h/cpp). Add sdf_gradient.h with finite-difference gradient utilities. Add Python modules vde.sdf (high-level SDF API) and vde.torch_sdf (PyTorch autograd). Add test_sdf_torch_bridge.cpp with batch eval/gradient tests. Integrate into vde_sdf library and test suite.