publish-canvas-image has been failing on every main push since 2026-04-21
at `addgroup -g 1000 canvas` because node:20-alpine already ships a `node`
user/group at uid/gid 1000. Same collision workspace-server/Dockerfile.tenant
already fixes with `deluser --remove-home node` before `addgroup`.
Copying that pattern here so the workflow goes green again and canvas images
publish to ghcr. No runtime behaviour change — canvas still runs as non-root
uid 1000.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>