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/error.rs

@@ -20,6 +20,9 @@ pub enum WorkflowError {
 
     #[error("表达式求值失败: {0}")]
     ExpressionError(String),
+
+    #[error("版本冲突: 数据已被其他操作修改，请刷新后重试")]
+    VersionMismatch,
 }
 
 impl From<sea_orm::TransactionError<WorkflowError>> for WorkflowError {
@@ -42,6 +45,7 @@ impl From<WorkflowError> for AppError {
             WorkflowError::InvalidDiagram(s) => AppError::Validation(s),
             WorkflowError::InvalidState(s) => AppError::Validation(s),
             WorkflowError::ExpressionError(s) => AppError::Validation(s),
+            WorkflowError::VersionMismatch => AppError::VersionMismatch,
         }
     }
 }