Add image extraction functionality with background removal

- Implemented ExtractImageRegion operator for extracting image regions using box or lasso selection.
- Added RemoveImageRegionBackground job for background removal from selected image regions.
- Created utility functions for polygon bounds, selection canvas creation, and applying selection masks.
- Integrated image processing using PIL and numpy for efficient pixel manipulation.
- Enhanced user experience with modal drawing and status updates during extraction.

docs/server.md

@@ -59,6 +59,8 @@ Environment 使用 Python 3.12、ONNX Runtime、NumPy、Pillow、PyAV、trimesh
 
 Balloon 的 `analyze-balloon` Job 会裁切套索输入并清零选区外 RGBA。`Contour` 用 BEN2 回传最大连通轮廓；`Depth` 用 MoGe-2 对有效相机距离稳健拟合二维基面，并把物理距离换算为不受绝对拍摄距离影响、未截断的相对深度信号。Job 同时把 MoGe normal 转换为 tangent-space 纹理，铺回原图尺寸并以中性法线填充无效区域。Blender 主线程负责采样深度属性、创建 Base Plane Empty、组装 `O Balloon Shape` 修改器与 `O Balloon Layer` 材质。
 
+图片 Box、Lasso 与 Perspective 的可选 `Remove Background` 使用 `extract-image-background` Job。它与标准 `remove-background` Job 共用单图 BEN2 去背景函数，再叠加图片工具专属的 polygon mask、局部 bounds 与透明 Padding。
+
 正式功能支持：
 
 - MoGe-2 ViT-S、ViT-B、ViT-L Normal