#27 Issue 27: [Events] Track Beneficiary and Delegate Changes

Description:
To maintain a perfect audit trail on the backend, the indexer needs to know if the ownership or delegate permissions of a vault change mid-stream.
Acceptance Criteria:

[ ] Emit BeneficiaryUpdated(vault_id, old_address, new_address).

[ ] Emit DelegateUpdated(vault_id, old_delegate, new_delegate).
Labels: events, data