Add image selection refinement functionality with BEN2 integration

- Implemented viewport.py for handling 3D view projections, gestures, and overlay drawing.
- Created refine_image_selection.py to manage the refinement of gesture masks and output image bounds.
- Added selection module with refine_selection.py to process and crop images based on alpha channel visibility.
- Introduced __init__.py for selection module to expose refine_selection function.

docs/internals/operators/index.md

@@ -8,7 +8,7 @@
 | `operators/ai_setup.py` | [AI 环境管理](ai-setup.md) | 环境安装、模型下载与缓存释放 |
 | `operators/clipboard_image/` | [Clipboard Image](clipboard-image.md) | 系统剪贴板读取、粘贴与快捷键 |
 | `operators/convert_to_plane/` | [Convert to Plane](convert-to-plane.md) | Mesh Plane 与 Depth Plane 创建 |
-| `operators/cutout_tool/` | [Cutout Tool](cutout-tool.md) | Region 选择、基础 Shape 构建与 Blender 对象创建 |
+| `operators/cutout_tool/` | [Cutout Tool](cutout-tool.md) | Selection、基础 Shape 构建与 Blender 对象创建 |
 | `operators/debug.py` | [Debug Operator](debug.md) | 模型接口与原始产物验证 |
 | `operators/image_tool/` | [Image Tool](image-tool.md) | Box、Lasso、Line 与 Polyline 编辑 |
 | `operators/perspective_tool/` | [Perspective Tool](perspective-tool.md) | 四点透视框与透视校正 |