Refactor geometry generation to standardize Blender object coordinates

- Unified the canonical local frame for generated geometries (Plane, Depth Plane, Relief Plane, Cutout, Depth Cutout) to align with Blender's object coordinate system, setting X as horizontal, Z as up, and +Y as depth.
- Removed the `Depth Axis` parameter from `O Image Cutout` and `O Image Depth Cutout`, simplifying the geometry generation process.
- Updated the depth direction defaults to use +Y instead of -Z for `O Image Relief Plane` and Depth Symmetry.
- Adjusted the geometry nodes to ensure thickness, projection, and shell displacements operate along the Y-axis.
- Implemented new capabilities for handling object space normals to align with the new canonical frame.
- Enhanced the Depth Symmetry functionality to mirror across the canonical Y-axis and perform a final rotation to maintain the correct orientation.
- Added tests to validate the new coordinate system and ensure compatibility with existing assets.

openspec/changes/standardize-blender-object-coordinates/specs/object-space-normal-alignment/spec.md

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+## ADDED Requirements
+
+### Requirement: Object Space Normal follows the canonical object frame
+
+系统 SHALL 让 Plane、Depth Plane、Relief Plane、Cutout 与 Depth Cutout 的 Object Space Normal 贴图按新的 canonical Blender 对象坐标解释：X 为图片水平、Z 为 up、Y 为深度方向。Object Space Normal 渲染结果 MUST 与最终 evaluated geometry 的几何法线方向一致。
+
+#### Scenario: Depth object uses Object Space Normal
+
+- **WHEN** Depth Plane 或 Depth Solid 使用 Object Space Normal 贴图渲染
+- **THEN** 平面法线朝向 -Y
+- **AND** 深度表面产生的 normal 变化围绕 -Y 基准
+- **AND** 渲染 normal 不再按旧 `-Z` 基准解释
+
+### Requirement: Depth Symmetry normal maps follow mirror and final orientation
+
+`O Image Cutout Symmetry` SHALL 为 Object Space Normal 提供最终朝向所需的面属性。材质 SHALL 对 canonical front 保持 normal，对 canonical back 反射 Y 分量，并应用最终 yaw 旋转；侧壁 SHALL 关闭 normal map 影响。
+
+#### Scenario: Front, back, and wall normals
+
+- **WHEN** Depth Symmetry 对象启用 Object Space Normal 并分别渲染 front、back 和 side wall
+- **THEN** front normal 按 canonical 方向解释
+- **AND** back normal 的 Y 分量相对 front 发生反射
+- **AND** 最终 X 朝向旋转被应用
+- **AND** side wall 不显示 Object Space Normal 细节
+
+### Requirement: Old Depth Axis normal compensation is removed
+
+材质和 normal-map 辅助代码 MUST 不再为 `O Image Cutout` 或 `O Image Depth Cutout` 的旧 `Depth Axis=+X` 提供 `CUTOUT_Z_TO_X` 补偿。Object Normal 的最终轴向转换 SHALL 只来自 Depth Symmetry 的新朝向属性。
+
+#### Scenario: Inspect normal transform attributes
+
+- **WHEN** 检查 `O Image Layer` 使用的 Object Normal 转换逻辑
+- **THEN** 不存在以旧 `Depth Axis` 为输入的轴向补偿
+- **AND** Depth Symmetry 的最终朝向属性由 `O Image Cutout Symmetry` 写入
+- **AND** 材质按该属性执行最终 normal 旋转