WDSP spectral noise blanker (SNBA) in WebAssembly

Runs snb_lite_* from web/dist/nnr_<variant>.js on data/clicks_16k.wav (speech + synthetic clicks), compares with the native nnr-lite output (build-linux/snb_lite_16000.f64, made by test/run_snb_compare.sh) and measures the cost of SNB, NNR and SNB→NNR. Everything stays on this machine.

variant passes