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-message/src/service/message_service.rs

@@ -218,9 +218,11 @@ impl MessageService {
             return Ok(());
         }
 
+        let current_version = model.version;
         let mut active: message::ActiveModel = model.into();
         active.is_read = Set(true);
         active.read_at = Set(Some(Utc::now()));
+        active.version = Set(current_version + 1);
         active.updated_at = Set(Utc::now());
         active.updated_by = Set(user_id);
         active
@@ -275,7 +277,9 @@ impl MessageService {
             ));
         }
 
+        let current_version = model.version;
         let mut active: message::ActiveModel = model.into();
+        active.version = Set(current_version + 1);
         active.deleted_at = Set(Some(Utc::now()));
         active.updated_at = Set(Utc::now());
         active.updated_by = Set(user_id);
@@ -308,6 +312,7 @@ impl MessageService {
             sent_at: m.sent_at,
             created_at: m.created_at,
             updated_at: m.updated_at,
+            version: m.version,
         }
     }
 }