M48: harden demo operations and offsite recovery

backend/entrypoint.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 set -e
 
-alembic upgrade head
+if [ "${RUN_MIGRATIONS:-true}" = "true" ]; then
+  alembic upgrade head
+fi
 exec uvicorn app.main:app --host 0.0.0.0 --port 8000