Send initial "check" event immediately (just domain name), then
resolve IPs, find routes, fetch whois and gateway checks all run
in parallel. Each result streams via its own SSE event:
- resolve: IPs + routes
- gateway: per-gateway availability
- whois: domain registration info
- throttle: slow download detection

Eliminates all delay before first visible response.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>