Dedupe by exit IP

Paste one proxy per line. Each line is checked through the proxy. We keep the first line per unique public exit IP.

Each line tries multiple IP echo URLs until one works. Mode 2 suits gateways that block JSON APIs or choke on bursts (e.g. Gonzo). Server-wide parallelism defaults to 500 concurrent exit checks (DEDUPE_MAX_CONCURRENT, max 4000); restart the app after changing it.