Linter-contributed improvements: - EnsureCentralService() method: registers Central's own domain as a service from config, with cleanup on domain change - Tests for EnsureCentralService: registration, idempotency, domain change cleanup, no-domain-is-noop - Improved reconciliation tests with Central as a registered service - Certbot handler cleanup Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>