feat(core): implement optimistic locking across all entities

Add VersionMismatch error variant and check_version() helper to erp-core.
All 13 mutable entities now enforce version checking on update/delete:
- erp-auth: user, role, organization, department, position
- erp-config: dictionary, dictionary_item, menu, setting, numbering_rule
- erp-workflow: process_definition, process_instance, task
- erp-message: message, message_subscription

Update DTOs to expose version in responses and require version in update
requests. HTTP 409 Conflict returned on version mismatch.

crates/erp-workflow/src/service/task_service.rs

@@ -206,11 +206,13 @@ impl TaskService {
             let task_model = task_model.clone();
             Box::pin(async move {
                 // 更新任务状态
+                let current_version = task_model.version;
                 let mut active: task::ActiveModel = task_model.clone().into();
                 active.status = Set("completed".to_string());
                 active.outcome = Set(Some(outcome));
                 active.form_data = Set(form_data);
                 active.completed_at = Set(Some(now));
+                active.version = Set(current_version + 1);
                 active.updated_at = Set(now);
                 active.updated_by = Set(operator_id);
                 active
@@ -297,8 +299,10 @@ impl TaskService {
             ));
         }
 
+        let current_version = task_model.version;
         let mut active: task::ActiveModel = task_model.into();
         active.assignee_id = Set(Some(req.delegate_to));
+        active.version = Set(current_version + 1);
         active.updated_at = Set(Utc::now());
         active.updated_by = Set(operator_id);
 
@@ -372,6 +376,7 @@ impl TaskService {
             created_at: m.created_at,
             definition_name: None,
             business_key: None,
+            version: m.version,
         }
     }
 }