oven/bun Base Image Has Existing Non-Root User

Applies when: adding non-root user to any Dockerfile that uses oven/bun as base image (Remotion service, or future Bun-based services).

oven/bun:1.3.10 ships with a bun user (UID 1000) and bun group (GID 1000).
Home directory is /home/bun, shell is /bin/sh.
Do NOT create a new app user with groupadd/useradd -- GID 1000 collision causes groupadd: GID '1000' already exists build failure.
Instead: RUN chown -R bun:bun /app then USER bun.
Verified: container runs as uid=1000(bun) gid=1000(bun), /app/out is writable.