fix: remove read-only flag from content volume to allow admin saves

The content volume was mounted as :ro (read-only) which prevented
the admin panel from writing gallery.yaml and settings.yaml changes.
Removed the :ro flag so the admin panel can save config and create backups.

docker-compose.yml

@@ -11,4 +11,4 @@ services:
       - path: .env.local
         required: false
     volumes:
-      - ./content:/app/content:ro
+      - ./content:/app/content