Crisp Webhook

Crisp Website Hook target. Authenticated via ?secret=. Acks fast and runs the bot as a Starlette BackgroundTask so Crisp isn't kept waiting.

(We use BackgroundTasks, not a bare asyncio.create_task: Starlette keeps a strong reference and runs it after the response, so it can't be garbage- collected mid-flight — a bare create_task we don't hold a ref to gets GC'd and cancelled intermittently, silently dropping replies.)