Add new node asset scripts for geometry and shader operations

- Implemented `build_mesh_plane.py` to create a geometry node group for mesh planes with customizable parameters.
- Created `build_shadeless.py` for a shader node group that displays color without scene lighting while preserving shadows and reflections.
- Added `validate.py` to validate the integrity of the newly created node groups and their inputs.
- Introduced `validate_cutout.py` to ensure the functionality of cutout node groups and their dependencies.
- Developed `validate_mesh_plane.py` to test the mesh plane creation and its modifier settings.

docs/internals/operators/index.md

@@ -0,0 +1,18 @@
+# Operator 实现索引
+
+`src/anyimage/operators/` 负责 Blender 侧交互、Job 请求组装和结果导入。内部实现按完整功能包或顶层业务模块拆页；只提供共享能力的 `common/` 不单独成页，其职责统一放在[程序架构](../architecture.md)中说明。
+
+| Operator 路径 | 实现页 | 主要职责 |
+| --- | --- | --- |
+| `operators/__init__.py` | 本页 | 汇总 Blender 类型注册顺序 |
+| `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) | 区域选择、轮廓生成与 Shape 构建 |
+| `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 |
+| `operators/remove_background.py` | [Remove Background](remove-background.md) | BEN2 去背与结果替换 |
+| `operators/upscale.py` | [Upscale](upscale.md) | 4× 高清与原图引用维护 |
+
+`operators/__init__.py` 只聚合注册类，不承载独立业务流程。具体类的注册和逆序注销由扩展入口统一管理，整体边界见[程序架构](../architecture.md)。