audiobookshelf: switch audiobooks mount from Docker NFS volume to systemd automount bind mount

NFS named volumes go ESTALE when unRAID drives spin down and Docker cannot recover.
systemd automount handles NFS reconnection transparently; Docker just sees a bind mount.

audiobookshelf/docker-compose.yaml

@@ -3,14 +3,6 @@ networks:
     external:
       name: npm-network
 
-volumes:
-  audiobooks:
-    driver: local
-    driver_opts:
-      type: nfs
-      o: "addr=192.168.1.192,rw,nolock,soft"
-      device: ":/mnt/user/media/audiobooks"
-
 services:
   audiobookshelf:
     image: ghcr.io/advplyr/audiobookshelf:latest
@@ -25,7 +17,7 @@ services:
     volumes:
       - /srv/audiobookshelf/config:/config
       - /srv/audiobookshelf/metadata:/metadata
-      - audiobooks:/audiobooks
+      - /mnt/nas_audiobooks:/audiobooks
     ports:
       - 13378:80
     restart: unless-stopped