Add comprehensive tests for image processing nodes and refactor node imports

- Introduced new test files for image layer, image plane, normal scale, object normal rotation, shadeless, and temporary attributes.
- Implemented tests to validate the behavior of alpha curves, depth layers, and normal scales in various rendering engines.
- Refactored import paths for node groups to align with the new directory structure.
- Added checks for temporary attribute lifetimes and ensured proper cleanup without warnings.
- Enhanced CLI commands to require the Blender group and validate the presence of generated node assets before packaging.
- Updated packaging scripts to enforce the existence of necessary assets, preventing build failures.

openspec/changes/separate-node-sources-and-tools/specs/generated-node-assets/spec.md

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+## ADDED Requirements
+
+### Requirement: Node asset is generated from source
+
+系统 SHALL 能够仅根据版本控制中的 `nodes/` 定义和 `tools/nodes` 构建工具生成 `src/anyimage/assets/O_AnyImage.blend`。生成文件 SHALL 不纳入 Git 版本控制。
+
+#### Scenario: Build from a clean checkout
+- **WHEN** 干净源码检出中不存在 `O_AnyImage.blend` 并执行节点资产构建
+- **THEN** 构建成功生成包含全部既定节点组的资产文件
+
+#### Scenario: Rebuild an existing asset
+- **WHEN** 输出路径已有本地生成的节点资产并再次执行构建
+- **THEN** 文件被当前源码生成的完整资产替换，不产生 `.blend1` 备份
+
+### Requirement: CI validates generated node assets
+
+测试 CI SHALL 通过统一的 `node-group` 入口和固定版本的 `bpy` wheel，在运行节点资产相关测试前生成并独立校验节点资产，不得要求额外的 Blender 应用程序安装。
+
+#### Scenario: Validate a pull request
+- **WHEN** 测试工作流检出不含节点资产的源码
+- **THEN** 工作流生成资产、校验保存结果并运行读取该资产的测试
+
+#### Scenario: Reject an invalid generated asset
+- **WHEN** 节点源码生成的资产未通过接口、结构或基本求值检查
+- **THEN** CI 在运行后续发布步骤前失败
+
+### Requirement: Release packages contain the generated asset
+
+发布 CI SHALL 在测试和打包前生成并验证节点资产。每个平台扩展归档 MUST 包含 `assets/O_AnyImage.blend`，打包器 MUST 在资产缺失时明确失败。
+
+#### Scenario: Package a release
+- **WHEN** 发布工作流从干净源码构建扩展
+- **THEN** 每个平台归档包含本次工作流生成并验证的节点资产
+
+#### Scenario: Package without building assets
+- **WHEN** 打包器运行时 `O_AnyImage.blend` 不存在
+- **THEN** 打包立即失败并提示先构建节点资产