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-auth/src/service/auth_service.rs

@@ -122,6 +122,7 @@ impl AuthService {
             avatar_url: user_model.avatar_url,
             status: user_model.status,
             roles: role_resps,
+            version: user_model.version,
         };
 
         // 9. Publish event
@@ -193,6 +194,7 @@ impl AuthService {
             avatar_url: user_model.avatar_url,
             status: user_model.status,
             roles: role_resps,
+            version: user_model.version,
         };
 
         Ok(LoginResp {
@@ -245,6 +247,7 @@ impl AuthService {
                 code: r.code.clone(),
                 description: r.description.clone(),
                 is_system: r.is_system,
+                version: r.version,
             })
             .collect())
     }