v0.19.2 New webhook: contract_holder.policy_issued

A new outbound webhook - SafetyWing sends an HTTP POST to your registered URL when a contract holder's policy is issued. It's delivered as a self‑describing envelope ({id, topic, companyId, payload}), with the event data under payload. Acknowledge with any 2xx.

Currently emitted for a dependant added to an already‑active member (contractHolderType=DEPENDENT, applicationType=POST_APPLICATION); the payload includes the contract/plan details (plan, policy id, start date, price, etc.).

Note: the legacy member.status_changed webhook (bare payload, no envelope) is deprecated - migrate to the contract‑based events like contract_holder.policy_issued.