feat(core): implement event outbox persistence

Add domain_events migration and SeaORM entity. Modify EventBus::publish
to persist events before broadcasting (best-effort: DB failure logs
warning but still broadcasts in-memory). Update all 19 publish call
sites across 4 crates to pass db reference.

Add outbox relay background task that polls pending events every 5s
and re-broadcasts them, ensuring no events are lost on server restart.

crates/erp-config/src/service/setting_service.rs

@@ -117,7 +117,7 @@ impl SettingService {
                     "key": params.key,
                     "scope": params.scope,
                 }),
-            ));
+            ), db).await;
 
             audit_service::record(
                 AuditLog::new(tenant_id, Some(operator_id), "setting.upsert", "setting")
@@ -158,7 +158,7 @@ impl SettingService {
                     "key": params.key,
                     "scope": params.scope,
                 }),
-            ));
+            ), db).await;
 
             audit_service::record(
                 AuditLog::new(tenant_id, Some(operator_id), "setting.upsert", "setting")