Listen on 0.0.0.0 by default and log LAN addresses

- New CANON_HOST (default 0.0.0.0; 127.0.0.1 keeps it on one machine)
- On start, log the http:// addresses other devices can use, skipping
  Docker/VM bridge interfaces
- docker-compose publishes 0.0.0.0:4242 explicitly
- README: opening Canon from other devices and firewall note

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker-compose.yml

@@ -7,7 +7,9 @@ services:
     container_name: canon
     restart: unless-stopped
     ports:
-      - "4242:4242"
+      # 0.0.0.0 makes Canon reachable from other devices on your network.
+      # Use "127.0.0.1:4242:4242" to keep it on this machine only.
+      - "0.0.0.0:4242:4242"
     volumes:
       - canon-data:/data
     env_file: