feat: optional policy payout beneficiary + holder-only updates

- Policy.beneficiary Option<Address>; initiate_policy + set_beneficiary
- Payout to beneficiary.unwrap_or(holder); BeneficiaryUpdated events
- Tests: policy_beneficiary + initiate_policy/Claim fixture updates
- Backend: 9-arg golden vectors, BuildTransactionDto aligned with contract
- Frontend: policy detail page + beneficiary mismatch warning
- Remove obsolete tests/events.rs; fix duplicate contractimpl methods

Made-with: Cursor

Author: aji70

backend/package-lock.json

@@ -129,6 +129,11 @@ export interface PolicyDto {
    * Empty array if no claims exist.
    */
   claims: ClaimSummaryDto[];
+  /**
+   * Optional payout beneficiary (on-chain). When set, approved claim proceeds
+   * are sent here instead of the holder. Null/omitted means holder receives payout.
+   */
+  beneficiary: string | null;
   /**
    * Self-link for this policy resource.
    * @example "/policies/GABC.../1"
@@ -188,6 +193,7 @@ export function toPolicyDto(p: Policy, claims: Claim[]): PolicyDto {
       avg_ledger_close_seconds: 5,
     },
     claims: claims.map(toClaimSummaryDto),
+    beneficiary: p.beneficiary ?? null,
     _link: `/policies/${encodeURIComponent(p.holder)}/${p.policy_id}`,
   };
 }