docs: document ROS2 image save outputs

docs/en/source/camera_devices/4_application_guide/services.md

@@ -331,6 +331,7 @@ On Gemini 330 series devices with firmware `1.8.21` or later, the following serv
     ```bash
     ros2 service call /camera/save_images std_srvs/srv/Empty '{}'
     ```
+    The service saves frames from each enabled image stream, up to the configured `max_save_images_count` (default `10`). For every frame, the node writes matching `.raw`, `.png`, and metadata `.json` files under the `image` directory in the current working directory. File names include the stream, resolution, frame rate, local timestamp with microsecond precision, and frame index.
 *   `/camera/save_point_cloud`
     ```bash
     ros2 service call /camera/save_point_cloud std_srvs/srv/Empty '{}'

docs/zh/source/camera_devices/4_application_guide/services.md

@@ -332,6 +332,7 @@ Gemini 330 系列设备使用固件 `1.8.21` 及以上版本时，如果设备
     ```bash
     ros2 service call /camera/save_images std_srvs/srv/Empty '{}'
     ```
+    该服务会为每个已启用的图像流保存帧，数量受 `max_save_images_count` 限制（默认值为 `10`）。每帧都会在当前工作目录下的 `image` 目录中生成对应的 `.raw`、`.png` 和元数据 `.json` 文件。文件名包含流名称、分辨率、帧率、带微秒精度的本地时间戳和帧序号。
 *   `/camera/save_point_cloud`
     ```bash
     ros2 service call /camera/save_point_cloud std_srvs/srv/Empty '{}'