Milestone 1 of #132. Adds docker-compose.yml with prod + staging services,
.env.example for port/data configuration, and Caddyfile.staging for HTTP-only
staging proxy. No changes to Dockerfile or server.js — same image, different
config.
Fixes#132 (partially)
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
