Revenuecat Webhook

Single entry point for all RevenueCat webhook events.

RevenueCat sends every event for the app to this one endpoint regardless of product. Each domain service owns its own product-id/event-type filtering and no-ops on events that aren't relevant to it, so the event is simply handed to every domain that consumes RevenueCat events.

Processing is awaited rather than backgrounded, and unexpected errors are intentionally left to propagate (see each service's handle_* method) so a genuine failure surfaces as a non-2xx response and RevenueCat retries delivery. All DB writes here are idempotent, so a retry is always safe -- this also means a crash mid-processing just results in RC redelivering, rather than the event being silently lost.