Erase everything Whisperr stores about a user

Data subject erasure (DPA section 8). Deletes, in one transaction, the user and every row that holds the user's data: profile and traits, state, channels, consent, events (also those stored only under the external id), evaluations, decisions, generated messages and their AI call records, outbound and relay messages with provider events, exposures, source identities, ingress deliveries, queued jobs, ingestion dead letters, and RevenueCat billing rows (also unlinked ones that match the external id). Records the request with a keyed hash of the external id only. Idempotent: a repeat answers 200 with found: false. Data sent for the same external id afterwards creates a new user. Server key only.