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/outputs.md

@@ -9,6 +9,7 @@
 | `generate-depth` | `results.npz`、深度与颜色序列 | Depth Plane 所需深度、相机和贴图 |
 | `generate-surface` | `mesh.npz`、`normal.png`、颜色层 | Surface 网格、相机与材质输入 |
 | `remove-background` | `color.0001.png` 起 | 带 Alpha 的颜色层 |
+| `extract-image-background` | `selection-input.png`、`image.png`、`bounds.json` | 图片工具选区内去背景后的局部图片与原图坐标 bounds |
 | `analyze-balloon` | `lasso-input.png`，按选项输出 `foreground.png`、`contour.json`、`depth.npz`、`normal.png` | 套索约束输入、BEN2 轮廓与 MoGe-2 深度、法线 |
 | `debug-da3` | `prediction.npz` | DA3 API 返回 |
 | `debug-moge2` | `prediction*.npz` | MoGe-2 API 返回 |