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-workflow/src/service/definition_service.rs

@@ -107,7 +107,7 @@ impl DefinitionService {
             "process_definition.created",
             tenant_id,
             serde_json::json!({ "definition_id": id, "key": req.key }),
-        ));
+        ), db).await;
 
         audit_service::record(
             AuditLog::new(tenant_id, Some(operator_id), "process_definition.create", "process_definition")
@@ -245,7 +245,7 @@ impl DefinitionService {
             "process_definition.published",
             tenant_id,
             serde_json::json!({ "definition_id": id }),
-        ));
+        ), db).await;
 
         audit_service::record(
             AuditLog::new(tenant_id, Some(operator_id), "process_definition.publish", "process_definition")