The multi-stage Dockerfile copies frontend/yarn.lock, but .gitignore
excluded it from the repo, breaking builds from a fresh clone (Coolify).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Multi-stage Dockerfile builds the email-builder, admin frontend, and Go
backend from source and stuffs assets into the binary. The runtime-only
image moved to Dockerfile.goreleaser for release builds. Adds a Coolify
compose file with magic service variables, healthchecks, and volumes.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>