feat: add Watchtower for automatic Docker image updates

- Created watch/compose.yaml with Watchtower service configuration
- Added Watchtower environment variables to arty.yml
- Enabled Watchtower monitoring for sexy_frontend container
- Configurable via environment variables (poll interval, cleanup, logging)
- Label-based updates: only containers with watchtower.enable=true

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

sexy/compose.yaml

@@ -86,6 +86,7 @@ services:
       - 'traefik.http.routers.${SEXY_COMPOSE_PROJECT_NAME}-frontend-web-secure.middlewares=${SEXY_COMPOSE_PROJECT_NAME}-frontend-web-secure-compress'
       - 'traefik.http.services.${SEXY_COMPOSE_PROJECT_NAME}-frontend-web-secure.loadbalancer.server.port=3000'
       - 'traefik.docker.network=${NETWORK_NAME}'
+      - 'com.centurylinklabs.watchtower.enable=true'
 
 volumes:
   directus_uploads: