Promote the user-switch from a hardcoded `node` to a keyword arg
so callers can opt into root (or any other user) when needed.
Default stays `node` — matches the docker image's USER and the
smolmachines runuser default.
Lifts the change through the base ABC, docker, and smolmachines
backends:
- Base: `def exec(self, script, *, user="node")`.
- Docker: adds `-u <user>` to `docker exec` (no-op when user is
node, the image's default).
- Smolmachines: `runuser -l <user> -c <script>` — `runuser -l
root` is the trivial no-op form when the caller asked for root.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
didericis-claude
af65c10361