Refactor Cutout and Image Editing Logic

- Renamed "Base Plane Depth" to "Reference Depth" across validate_cutout.py for consistency.
- Introduced a new specification for Cutout mesh sampling to ensure source pixel spacing is preserved and limits are applied correctly.
- Unified naming conventions for image editing results to maintain consistency across Remove Background, Upscale, and Crop operations.
- Updated the handling of Refine Selection to ensure it retains the original bounds and does not apply unnecessary cropping.
- Enhanced material generation logic to connect image color directly to IOR Level, improving the rendering of dark areas.
- Established clear requirements for geometry depth controls and image result materials to ensure consistent behavior across different components.
- Removed outdated logic and ensured all changes are documented and tested for regression.

docs/internals/node-assets.md

@@ -41,6 +41,8 @@ uv run build_node --skip-tests
 
 `O Image Cutout` 在四个 Shape 分支与平滑之后统一处理 **Inward Axis**。Shape 子节点保持内部 `+X` 朝向；默认 `-Z` 分支执行一次轴转换，`+X` 分支保留内部坐标。运行时对象矩阵与该接口配对，保证两种模式落在相同世界空间位置。
 
+`O Image Depth Plane`、`O Image Cutout`、`O Image Depth Balloon` 与 `O Image Depth Surface` 统一使用 **Reference Depth** 作为采样深度的运算基准。
+
 ## 修改节点组
 
 1. 修改 `tools/node_assets/build_*.py`；