Remove named volume from prod compose, use bind mount for notebooks

The base docker-compose.yml already mounts ./notebooks:/app/notebooks.
The named Docker volume was shadowing it in prod, preventing example
notebooks from being visible. Bind mount ensures examples ship with
the repo and user notebooks persist on the host filesystem.

docker-compose.prod.yml

@@ -4,8 +4,6 @@ services:
       context: ./backend
       dockerfile: Dockerfile
       target: prod
-    volumes:
-      - notebooks:/app/notebooks
     expose:
       - "8000"
     networks:
@@ -30,9 +28,6 @@ services:
       caddy: "${SPICEBOOK_DOMAIN:-spicebook.localhost}"
       caddy.reverse_proxy_1: "{{upstreams 4321}}"
 
-volumes:
-  notebooks:
-
 networks:
   caddy:
     external: true