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.
茂之钳