Switch the production stage to the built-in node user from
node:lts-trixie-slim, fixing two runtime failures:
1. Claude CLI rejects --dangerously-skip-permissions when the
process UID is 0, making the claude-local adapter unusable.
2. The server crashed at startup (EACCES) because /paperclip was
root-owned and the process could not write logs or instance data.
Changes vs the naive fix:
- Use COPY --chown=node:node instead of a separate RUN chown -R,
avoiding a duplicate image layer that would double the size of
the /app tree in the final image.
- Consolidate mkdir /paperclip + chown into the same RUN layer as
the npm global install (already runs as root) to keep layer count
minimal.
- Add USER node before CMD so the process runs unprivileged.
The VOLUME declaration comes after chown so freshly-mounted
anonymous volumes inherit the correct node:node ownership.
Fixes#344
