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-config/src/handler/theme_handler.rs

@@ -59,6 +59,7 @@ where
             scope: "tenant".to_string(),
             scope_id: None,
             value,
+            version: None,
         },
         ctx.tenant_id,
         ctx.user_id,