v0.3.1

Default output dir is roots/; re-scope DESIGN.md to internals

The emitted directories are root modules — own backend, providers,
state — so --out now defaults to roots/, leaving modules/ free for
reusable child modules. DESIGN.md drops what the README owns and
keeps concepts and internals; stale claims fixed across DESIGN.md
and LIMITATIONS.md (guarded push exists, resume machinery is gone,
fixture list, message quotes).

+semver: patch

## Release Notes

<!-- release-notes -->
The default `--out` directory is now `roots/` (was `modules/`): what demonolith writes are root modules — each with its own backend, providers, and state — and `modules/` stays free for reusable child modules. Pass `--out modules` to keep the old layout.
<!-- /release-notes -->