fix: resolve volume permission error for non-root container user

Entrypoint now runs as root, chowns the data directory to appuser,
then drops privileges via gosu before starting Gunicorn. This prevents
sqlite3.OperationalError on mounted volumes owned by root.

entrypoint.sh

@@ -1,7 +1,12 @@
 #!/bin/sh
+# Fix ownership of the data directory so appuser can write the database.
+# This runs as root (no USER directive in Dockerfile) and is safe because
+# we immediately drop privileges via gosu before starting the app.
+DATA_DIR=$(dirname "${DATABASE_PATH:-/data/guestbook.db}")
+chown -R appuser:appuser "$DATA_DIR"
+
 # Process index.html.template to create index.html
-# Adjust the path if your template is located somewhere else
 envsubst < /app/templates/index.html.template > /app/templates/index.html
 
-# Start Gunicorn; using an environment variable for workers (default is 3)
-exec gunicorn --bind 0.0.0.0:8000 app:app --workers ${GUNICORN_WORKERS:-3}
+# Drop to appuser and start Gunicorn
+exec gosu appuser gunicorn --bind 0.0.0.0:8000 app:app --workers ${GUNICORN_WORKERS:-3}