fix: log volume permission errors instead of swallowing them

Previously chown errors were silently discarded. Now logs a warning so
users can diagnose permission issues with Docker volume mounts.

docker/entrypoint.sh

@@ -4,7 +4,8 @@ set -e
 # Fix ownership of mounted volumes so the non-root stirling user can write.
 # This runs as root, fixes permissions, then drops to stirling via gosu.
 if [ "$(id -u)" = "0" ]; then
-  chown -R stirling:stirling /data /tmp/workspace 2>/dev/null || true
+  chown -R stirling:stirling /data /tmp/workspace 2>&1 || \
+    echo "WARNING: Could not fix volume permissions. If processing fails, check your volume mount permissions." >&2
   exec gosu stirling "$@"
 fi