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-config/src/error.rs

@@ -41,3 +41,76 @@ impl From<ConfigError> for AppError {
 }
 
 pub type ConfigResult<T> = Result<T, ConfigError>;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use erp_core::error::AppError;
+
+    #[test]
+    fn config_error_validation_maps_to_app_validation() {
+        let app: AppError = ConfigError::Validation("字段不能为空".to_string()).into();
+        match app {
+            AppError::Validation(msg) => assert_eq!(msg, "字段不能为空"),
+            other => panic!("期望 Validation，实际得到 {:?}", other),
+        }
+    }
+
+    #[test]
+    fn config_error_not_found_maps_to_app_not_found() {
+        let app: AppError = ConfigError::NotFound("字典不存在".to_string()).into();
+        match app {
+            AppError::NotFound(msg) => assert_eq!(msg, "字典不存在"),
+            other => panic!("期望 NotFound，实际得到 {:?}", other),
+        }
+    }
+
+    #[test]
+    fn config_error_duplicate_key_maps_to_app_conflict() {
+        let app: AppError = ConfigError::DuplicateKey("编码已存在".to_string()).into();
+        match app {
+            AppError::Conflict(msg) => assert_eq!(msg, "编码已存在"),
+            other => panic!("期望 Conflict，实际得到 {:?}", other),
+        }
+    }
+
+    #[test]
+    fn config_error_numbering_exhausted_maps_to_app_internal() {
+        let app: AppError = ConfigError::NumberingExhausted("序列已耗尽".to_string()).into();
+        match app {
+            AppError::Internal(msg) => assert!(msg.contains("序列已耗尽")),
+            other => panic!("期望 Internal，实际得到 {:?}", other),
+        }
+    }
+
+    #[test]
+    fn config_error_version_mismatch_maps_to_app_version_mismatch() {
+        let app: AppError = ConfigError::VersionMismatch.into();
+        match app {
+            AppError::VersionMismatch => {}
+            other => panic!("期望 VersionMismatch，实际得到 {:?}", other),
+        }
+    }
+
+    #[test]
+    fn config_error_display_messages() {
+        // 验证各变体的 Display 输出包含中文描述
+        assert!(ConfigError::Validation("test".into()).to_string().contains("验证失败"));
+        assert!(ConfigError::NotFound("test".into()).to_string().contains("资源未找到"));
+        assert!(ConfigError::DuplicateKey("test".into()).to_string().contains("键已存在"));
+        assert!(ConfigError::NumberingExhausted("test".into()).to_string().contains("编号序列耗尽"));
+        assert!(ConfigError::VersionMismatch.to_string().contains("版本冲突"));
+    }
+
+    #[test]
+    fn transaction_error_connection_maps_to_validation() {
+        // TransactionError::Connection 应该转换为 ConfigError::Validation
+        let config_err: ConfigError =
+            sea_orm::TransactionError::Connection(sea_orm::DbErr::Conn(sea_orm::RuntimeErr::Internal("连接失败".to_string())))
+                .into();
+        match config_err {
+            ConfigError::Validation(msg) => assert!(msg.contains("连接失败")),
+            other => panic!("期望 Validation，实际得到 {:?}", other),
+        }
+    }
+}