feat: add Authelia SSO authentication service

- Add Authelia service to NET stack for centralized SSO
- Create configuration.yml with PostgreSQL storage
- Create users_database.yml for file-based user management
- Add authelia database to PostgreSQL init script
- Configure Traefik ForwardAuth middleware
- Add environment variables to arty.yml
- Supports TOTP and WebAuthn 2FA
- Email notifications via Mailpit SMTP relay
- Protected services: netdata, mailpit, scrapy, restic, traefik, dev, n8n, asciinema, coolify

arty.yml

@@ -125,6 +125,9 @@ envs:
     # Mailpit SMTP Relay
     NET_MAILPIT_IMAGE: axllent/mailpit:latest
     NET_MAILPIT_TRAEFIK_HOST: mailpit.pivoine.art
+    # Authelia SSO
+    NET_AUTHELIA_IMAGE: authelia/authelia:latest
+    NET_AUTHELIA_TRAEFIK_HOST: auth.pivoine.art
     # AI Stack
     AI_TRAEFIK_ENABLED: true
     AI_COMPOSE_PROJECT_NAME: ai