test: add 149 unit tests across core, auth, config, message crates

Test coverage increased from ~34 to 183 tests (zero failures):

- erp-core (21): version check, pagination, API response, error mapping
- erp-auth (39): org tree building, DTO validation, error conversion,
  password hashing, user model mapping
- erp-config (57): DTO validation, numbering reset logic, menu tree
  building, error conversion. Fixed BatchSaveMenusReq nested validation
- erp-message (50): DTO validation, template rendering, query defaults,
  error conversion
- erp-workflow (16): unchanged (parser + expression tests)

All tests are pure unit tests requiring no database.

crates/erp-message/src/error.rs

@@ -43,3 +43,78 @@ impl From<sea_orm::TransactionError<MessageError>> for MessageError {
 }
 
 pub type MessageResult<T> = Result<T, MessageError>;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use erp_core::error::AppError;
+
+    #[test]
+    fn validation_maps_to_app_validation() {
+        let app: AppError = MessageError::Validation("标题不能为空".to_string()).into();
+        match app {
+            AppError::Validation(msg) => assert_eq!(msg, "标题不能为空"),
+            other => panic!("Expected AppError::Validation, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn not_found_maps_to_app_not_found() {
+        let app: AppError = MessageError::NotFound("消息不存在".to_string()).into();
+        match app {
+            AppError::NotFound(msg) => assert_eq!(msg, "消息不存在"),
+            other => panic!("Expected AppError::NotFound, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn duplicate_template_code_maps_to_app_conflict() {
+        let app: AppError = MessageError::DuplicateTemplateCode("WELCOME".to_string()).into();
+        match app {
+            AppError::Conflict(msg) => assert_eq!(msg, "WELCOME"),
+            other => panic!("Expected AppError::Conflict, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn template_render_error_maps_to_app_internal() {
+        let app: AppError = MessageError::TemplateRenderError("变量缺失".to_string()).into();
+        match app {
+            AppError::Internal(msg) => assert_eq!(msg, "变量缺失"),
+            other => panic!("Expected AppError::Internal, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn version_mismatch_maps_to_app_version_mismatch() {
+        let app: AppError = MessageError::VersionMismatch.into();
+        match app {
+            AppError::VersionMismatch => {}
+            other => panic!("Expected AppError::VersionMismatch, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn error_display_format() {
+        assert_eq!(
+            MessageError::Validation("字段为空".to_string()).to_string(),
+            "验证失败: 字段为空"
+        );
+        assert_eq!(
+            MessageError::NotFound("id=123".to_string()).to_string(),
+            "未找到: id=123"
+        );
+        assert_eq!(
+            MessageError::DuplicateTemplateCode("CODE".to_string()).to_string(),
+            "模板编码已存在: CODE"
+        );
+        assert_eq!(
+            MessageError::TemplateRenderError("解析失败".to_string()).to_string(),
+            "渲染失败: 解析失败"
+        );
+        assert_eq!(
+            MessageError::VersionMismatch.to_string(),
+            "版本冲突: 数据已被其他操作修改，请刷新后重试"
+        );
+    }
+}