Reversible AES-256-GCM encryption for registration tokens so the
install one-liner can auto-fill the token value again. Migration 049
adds token_encrypted column; token_hash kept for lookup.
AgentManagement.tsx gets platform cards (Linux, Windows; macOS = soon)
with generateInstallCommand for all platforms. Inert until backend lands.
system_event_logger.go extracted from deleted event_stream.go —
SystemEventLogger survives, unified substrate does not.
security_settings_service.go and secrets_manager.go simplified.
