feat(stack): add Paperless-ngx document management system

- Add paperless.yml stack (port 8091, documents.schweitz.net)
- Uses shared postgres (DB: paperless) and redis (DB 8)
- ClamAV installed on host for virus scanning (port 3310)
- Add Paperless integration to library-desk stack
- Update CONTAINERS.md with Paperless and ClamAV profiles
- Add Portainer and NPM API documentation to setup-new-host.md
- Update redis-shared.yml and postgres-shared.yml with Paperless refs

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

stacks/postgres-shared.yml

@@ -133,4 +133,5 @@ networks:
 #   - Authentik (identity provider)
 #   - Gitea (git hosting) - migrated from dedicated instance
 #   - Nextcloud (personal cloud storage) - migrated from MariaDB
+#   - Paperless-ngx (document management) - DB: paperless, User: paperless_user
 #   - Future applications as needed