Widgets entrypoint

Umbrella import for TorchLean's optional Infoview / widget tooling.

This entrypoint imports the widget implementation modules directly. We avoid a second top-level NN.Widgets alias so the root namespace stays focused on the library umbrella and subsystem entrypoints.

The entrypoint is intentionally editor-facing:

• ordinary runtime/proof files should import the concrete library modules they need;
• tutorial and inspection files can import this one module to get all widget commands;
• adding a widget here does not make it part of TorchLean's trusted semantics.

NN.Widgets.Interop.PyTorchTranslator is included here because it is exactly that kind of editor-side assistant: useful for navigating PyTorch-to-TorchLean workflows, but not a proof that arbitrary Python has been verified.