LibTorch Backend Capsules

Optional LibTorch-backed capsules.

These capsules are intentionally separated from the default registry. Enabling them means accepting an external implementation boundary. Its SDPA bridge uses TorchLean's hard boolean-mask convention. Forward-only and external-autograd paths are separate capsules so the planner can name the exact trust boundary.

def NN.Backend.LibTorch.capsules : List KernelCapsule

Optional LibTorch capsules currently known to the planner.