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/error.rs

@@ -14,6 +14,9 @@ pub enum ConfigError {
 
     #[error("编号序列耗尽: {0}")]
     NumberingExhausted(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<ConfigError>> for ConfigError {
@@ -34,6 +37,7 @@ impl From<ConfigError> for AppError {
             ConfigError::NotFound(s) => AppError::NotFound(s),
             ConfigError::DuplicateKey(s) => AppError::Conflict(s),
             ConfigError::NumberingExhausted(s) => AppError::Internal(s),
+            ConfigError::VersionMismatch => AppError::VersionMismatch,
         }
     }
 }