entrypoint: remove ghost directories before creating json files

entrypoint.sh

@@ -1,6 +1,13 @@
 #!/bin/sh
 set -e
-mkdir -p /app/data /app/assets/deck-images
-[ -f /app/data/colony.json ] || echo '{"games":[]}' > /app/data/colony.json
-[ -f /app/data/decks.json  ] || echo '{"decks":[]}'  > /app/data/decks.json
+
+mkdir -p /app/data /app/data/deck-images
+
+# Docker creates directories instead of files when a bind-mount target doesn't exist.
+# Remove them so we can create proper JSON files.
+for f in /app/data/colony.json /app/data/decks.json; do
+  [ -d "$f" ] && rm -rf "$f"
+  [ -f "$f" ] || echo '{}' > "$f"
+done
+
 exec node server.js