The Sample Foundry: turns a track URL into separated stems ready for
sampling, replacing the manual yt-dlp → demucs → Audacity dance.

- engine/ — pure-ish, importable steps (model/fetch/separate); heavy work
  shells out to dedicated venvs so the engine runs under system python3
- separate.py = pluggable backend REGISTRY: demucs (engine1, live) +
  roformer (engine2, stubbed) behind one --backend interface
- foundry.py — CLI driver (fetch/sep/catch/list/backends/serve), tide.py-style
- server.py — stdlib GUI backend with job-progress + HTTP Range (audio seek)
- ui/index.html — self-contained GUI in the armada Ship's Bridge tokens;
  stems colour-coded by role (bass/drums/other/vocals)
- tests/ — 10 unit tests on the pure parts (slug, info-parse, argv, registry)
- README — workflow, engine1→engine2 roadmap incl. Roformer hyperparams +
  6GB VRAM caveat, phase-2 loop-finder charter, UX surface

Validated end-to-end on the Loituma test catch.