LibTorch Backend Capsules

Optional LibTorch-backed capsules.

These capsules are intentionally separated from the maintained registry. Adding the module means accepting an external implementation boundary. The SDPA bridge uses TorchLean's hard boolean-mask convention and supplies forward values only; TorchLean retains the tape and local backward rule.

def NN.Backend.LibTorch.capsules : Array KernelCapsule

Optional LibTorch capsules currently known to the planner.