(config) Harden Docker deployment for remote servers

Run the Django control panel with Gunicorn instead of the development
runserver and serve static files through WhiteNoise.

Add restart policies, healthchecks, .env-driven production settings, and
a sample .env file for single-server deployments. Update the Docker
entrypoint to collect static assets and document the remote server
deployment and update flow in the README.

scripts/docker-entrypoint

@@ -4,5 +4,6 @@ set -eu
 mkdir -p "$(dirname "${POBSYNC_SQLITE_PATH:-/var/lib/pobsync/pobsync.sqlite3}")"
 
 python manage.py migrate --noinput
+python manage.py collectstatic --noinput --clear
 
 exec "$@"