add name volume and update error handling

docker-compose.yml

@@ -20,6 +20,9 @@ services:
       # Select host port via APP_PORT env var; default 3000
       - "${APP_PORT:-3000}:3000"
     volumes:
-      # Persist local cache JSON files
-      - ./data:/app/data
+      # Persist cache JSON files using a named volume
+      - magikarp-data:/app/data
     restart: unless-stopped
+
+volumes:
+  magikarp-data: