AMUT-FEAT-001 — Cross-network "download the torrent instead" intent handoff

[itlezy]

Part of the post-0.7.3 suite forward program (Phase 2, optional controller layer). Spec: https://github.com/emulebb/amutorrent/blob/main/docs/active/items/AMUT-FEAT-001.md
Roadmap: emulebb-tooling docs/active/SUITE-JOINT-ROADMAP.md