Pure tarball construction (_build_tarball, _render_*, _iter_included,
_SYSTEMD_UNITS) moved to decnet/swarm/bundle_builder.py — no FastAPI
dependency, independently testable. EnrollBundleRequest/Response moved
to decnet/web/db/models/swarm.py alongside the other swarm DTOs.
Router drops from 504 to 260 lines; keeps only the in-memory token
registry, sweeper, and endpoints.
