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/depth-symmetry-orientation/spec.md

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+## ADDED Requirements
+
+### Requirement: Depth Symmetry mirrors across the canonical Y axis
+
+`O Image Cutout Symmetry` SHALL 在 canonical Blender 对象坐标中沿 Y 轴镜像，即镜像面为 `Y=0` 的 XZ 平面。镜像前后的几何 MUST 在最终旋转前保持 `(x, y, z)` 与 `(x, -y, z)` 的对应关系。
+
+#### Scenario: Canonical mirroring
+
+- **WHEN** 上游 Depth Cutout 输出 canonical 几何并连接 `O Image Cutout Symmetry`
+- **THEN** 对称节点先按 Y 轴删除越界半侧并镜像到另一侧
+- **AND** Fill Sides 开启时沿 Y 方向连接对应边界
+
+### Requirement: Final symmetry axis is X with Z up
+
+`O Image Cutout Symmetry` SHALL 在 canonical Y 镜像完成后执行绕 Z 的固定旋转，使对称轴从 +Y 变为 +X，并保持 +Z 为 up。最终结果 MUST 在本地坐标中关于 `X=0` 对称。
+
+#### Scenario: Default Depth Symmetry result
+
+- **WHEN** 用户通过 Depth Symmetry 入口生成对象
+- **THEN** 最终 evaluated local geometry 关于 `X=0` 对称
+- **AND** 最终 Z 范围反映图片 up 范围
+- **AND** 对象保持 up=Z
+
+### Requirement: Depth Symmetry final front direction may change
+
+Depth Symmetry 的最终朝向 SHALL 允许 canonical front `-Y` 随最终 yaw 旋转变为 `-X`。系统 MUST 不要求 Depth Symmetry 最终继续满足 front=-Y。
+
+#### Scenario: Final front direction
+
+- **WHEN** 使用把 +Y 映射到 +X 的最终 yaw 旋转
+- **THEN** canonical front 方向 -Y 映射为 -X
+- **AND** up 方向 +Z 保持不变
+
+### Requirement: Depth Symmetry path has no Cutout Depth Axis
+
+Depth Symmetry 创建流程 SHALL 不设置或依赖 `O Image Depth Cutout` 的 `Depth Axis`。所有最终轴向语义 MUST 只由 `O Image Cutout Symmetry` 承担。
+
+#### Scenario: Create Depth Symmetry modifiers
+
+- **WHEN** 用户通过 Depth Symmetry 入口创建对象
+- **THEN** 上游 `O Image Depth Cutout` 不包含 `Depth Axis` 输入
+- **AND** 上游 Cutout 输出 canonical +Y 深度结果
+- **AND** `O Image Cutout Symmetry` 决定最终 X 朝向