plot_envelope.py grows a --show flag. With it, matplotlib's WebAgg backend
spins up a localhost server with a real interactive figure (zoom, pan,
hover, axes lock) — equivalent to a matlab plot window without needing
tkinter or Qt locally.
tools/show_envelope.sh is a NixOS-aware wrapper: it locates libstdc++.so.6
in /nix/store (numpy's prebuilt wheel needs it on LD_LIBRARY_PATH) and then
exec's the python script with --show. Default port 8988, override via
--port. Bound to 0.0.0.0 so the figure is reachable over WG too.
tornado is added to dev deps because WebAgg requires it.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
