Move probe execution from Django app ready() to gunicorn.conf.py
Remove threading implementation to simplify startup sequence
Ensure probe runs in worker process context with proper error handling
Reorganize Docker Compose services: the Django/gunicorn container is now
`app` and nginx is `web`, better reflecting their roles. Add a dedicated
gunicorn configuration and install curl in the runtime image for health
checks.
Update documentation to reflect:
- Neo4j migration from ariel.incus to a dedicated umbriel.incus instance
- Rationale for requiring a dedicated Neo4j instance (single-tenancy
assumptions, label/index isolation, schema ownership)
- New service naming in compose commands and log tailing examples
