Add Docker support with Gunicorn, SQLite volume persistence, and optional PostgreSQL

Co-authored-by: Cursor <cursoragent@cursor.com>

docker-entrypoint.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+set -e
+
+if [ -n "$DATABASE_URL" ]; then
+  until PGPASSWORD="${POSTGRES_PASSWORD:-accounting_password}" psql -h "${DB_HOST:-accounting-db}" -U "${POSTGRES_USER:-accounting_user}" -d "${POSTGRES_DB:-accounting_db}" -c '\q' 2>/dev/null; do
+    >&2 echo "PostgreSQL is unavailable - sleeping"
+    sleep 1
+  done
+  >&2 echo "PostgreSQL is up"
+fi
+
+python manage.py migrate --noinput
+
+exec "$@"