Parity test: browser extractor vs PyTorch LongSpanExtractor

Reference spans come from tests/make_ref.py (PyTorch, fp32, CPU). This page runs the same fields through the ONNX model in your browser and compares start/end offsets and the present/absent decision. URL options: ?set=quick|all|long, ?backend=wasm, ?repo=<url prefix>, ?onnx=<file>, ?auto=1.