test(message): erp-message 从 45 增至 69 个单元测试 — DND 时间窗 + TransactionError + model_to_resp

- module.rs: 提取 is_in_dnd_window 纯函数 + 14 个 DND 时间窗测试（正常范围/跨午夜/边界）
- error.rs: 2 个 TransactionError 转换测试（Connection/Transaction）
- message_service: 2 个 model_to_resp 字段映射测试
- template_service: 1 个 model_to_resp 字段映射测试
- subscription_service: 1 个 model_to_resp 字段映射测试

crates/erp-message/src/error.rs

@@ -117,4 +117,28 @@ mod tests {
             "版本冲突: 数据已被其他操作修改，请刷新后重试"
         );
     }
+
+    #[test]
+    fn transaction_connection_error_maps_to_validation() {
+        let db_err = sea_orm::DbErr::Conn(sea_orm::RuntimeErr::Internal("连接超时".to_string()));
+        let tx_err: sea_orm::TransactionError<MessageError> =
+            sea_orm::TransactionError::Connection(db_err);
+        let msg_err: MessageError = tx_err.into();
+        match msg_err {
+            MessageError::Validation(msg) => assert!(msg.contains("连接超时")),
+            other => panic!("期望 Validation，得到 {:?}", other),
+        }
+    }
+
+    #[test]
+    fn transaction_inner_error_passthrough() {
+        let inner = MessageError::NotFound("模板不存在".to_string());
+        let tx_err: sea_orm::TransactionError<MessageError> =
+            sea_orm::TransactionError::Transaction(inner);
+        let msg_err: MessageError = tx_err.into();
+        match msg_err {
+            MessageError::NotFound(msg) => assert_eq!(msg, "模板不存在"),
+            other => panic!("期望 NotFound，得到 {:?}", other),
+        }
+    }
 }